refactor: reduce e2e test duplication with parameterization and enhance CLI docs (#2675)

* refactor: update documentation for model generation options and examples

* refactor: enhance documentation for --output-model-type option and examples

* refactor: update documentation for --allof-merge-mode and --enum-field-as-literal options

* refactor: update output paths in enum literal tests

Author: koxudaxi

docs/cli-reference/field-customization.md

@@ -1339,29 +1339,58 @@ The `--field-extra-keys` flag configures the code generation behavior.
 
 ??? example "Output"
 
-    ```python
-    # generated by datamodel-codegen:
-    #   filename:  extras.json
-    #   timestamp: 2019-07-26T00:00:00+00:00
-    
-    from __future__ import annotations
-    
-    from typing import Optional
-    
-    from pydantic import BaseModel, Field
-    
-    
-    class Extras(BaseModel):
-        name: Optional[str] = Field(
-            None,
-            description='normal key',
-            example='example',
-            invalid_key_1='abc',
-            key2=456,
-            repr=True,
-        )
-        age: Optional[int] = Field(None, example=12, examples=[13, 20])
-    ```
+    === "Pydantic v1"
+
+        ```python
+        # generated by datamodel-codegen:
+        #   filename:  extras.json
+        #   timestamp: 2019-07-26T00:00:00+00:00
+        
+        from __future__ import annotations
+        
+        from typing import Optional
+        
+        from pydantic import BaseModel, Field
+        
+        
+        class Extras(BaseModel):
+            name: Optional[str] = Field(
+                None,
+                description='normal key',
+                example='example',
+                invalid_key_1='abc',
+                key2=456,
+                repr=True,
+            )
+            age: Optional[int] = Field(None, example=12, examples=[13, 20])
+        ```
+
+    === "Pydantic v2"
+
+        ```python
+        # generated by datamodel-codegen:
+        #   filename:  extras.json
+        #   timestamp: 2019-07-26T00:00:00+00:00
+        
+        from __future__ import annotations
+        
+        from typing import Optional
+        
+        from pydantic import BaseModel, Field
+        
+        
+        class Extras(BaseModel):
+            name: Optional[str] = Field(
+                None,
+                description='normal key',
+                examples=['example'],
+                json_schema_extra={'key2': 456, 'invalid-key-1': 'abc'},
+                repr=True,
+            )
+            age: Optional[int] = Field(
+                None, examples=[13, 20], json_schema_extra={'example': 12}
+            )
+        ```
 
 ---
 
@@ -1422,37 +1451,77 @@ in Field(). This is useful for custom schema extensions and vendor-specific meta
 
 ??? example "Output"
 
-    ```python
-    # generated by datamodel-codegen:
-    #   filename:  extras.json
-    #   timestamp: 2019-07-26T00:00:00+00:00
-    
-    from __future__ import annotations
-    
-    from typing import Optional
-    
-    from pydantic import BaseModel, Field
-    
-    
-    class Extras(BaseModel):
-        name: Optional[str] = Field(
-            None,
-            description='normal key',
-            example='example',
-            field_comment='comment',
-            field_exclude=123,
-            field_invalid_key_2='efg',
-            invalid_key_1='abc',
-            key1=123,
-            key2=456,
-            readOnly=True,
-            register_='hij',
-            repr=True,
-            schema_='klm',
-            x_abc=True,
-        )
-        age: Optional[int] = Field(None, example=12, examples=[13, 20], writeOnly=True)
-    ```
+    === "Pydantic v1"
+
+        ```python
+        # generated by datamodel-codegen:
+        #   filename:  extras.json
+        #   timestamp: 2019-07-26T00:00:00+00:00
+        
+        from __future__ import annotations
+        
+        from typing import Optional
+        
+        from pydantic import BaseModel, Field
+        
+        
+        class Extras(BaseModel):
+            name: Optional[str] = Field(
+                None,
+                description='normal key',
+                example='example',
+                field_comment='comment',
+                field_exclude=123,
+                field_invalid_key_2='efg',
+                invalid_key_1='abc',
+                key1=123,
+                key2=456,
+                readOnly=True,
+                register_='hij',
+                repr=True,
+                schema_='klm',
+                x_abc=True,
+            )
+            age: Optional[int] = Field(None, example=12, examples=[13, 20], writeOnly=True)
+        ```
+
+    === "Pydantic v2"
+
+        ```python
+        # generated by datamodel-codegen:
+        #   filename:  extras.json
+        #   timestamp: 2019-07-26T00:00:00+00:00
+        
+        from __future__ import annotations
+        
+        from typing import Optional
+        
+        from pydantic import BaseModel, Field
+        
+        
+        class Extras(BaseModel):
+            name: Optional[str] = Field(
+                None,
+                description='normal key',
+                examples=['example'],
+                json_schema_extra={
+                    'key1': 123,
+                    'key2': 456,
+                    '$exclude': 123,
+                    'invalid-key-1': 'abc',
+                    '-invalid+key_2': 'efg',
+                    '$comment': 'comment',
+                    'register': 'hij',
+                    'schema': 'klm',
+                    'x-abc': True,
+                    'readOnly': True,
+                },
+                repr=True,
+            )
+            age: Optional[int] = Field(
+                None, examples=[13, 20], json_schema_extra={'example': 12, 'writeOnly': True}
+            )
+        ```
 
 ---