[ghanashyam03]

Description

Closes #122

When requesting calibrated Level 1.5 SDO/AIA data from JSOC via the export system, users can specify the aia_scale_aialev1 processing step. Currently, drms only serialized processing options when given keyword arguments (key=value), but commands like aia_scale_aialev1 can be run without extra options, or with options like mpt=aia.master_pointing3h.

This PR improves export processing handling in HttpJsonClient._exp_request_url:

• Allows passing a single processing command name as a string (e.g. process="aia_scale_aialev1"), in addition to dictionaries and lists.
• Allows dictionary values to be None or empty dicts when no sub-arguments are needed (e.g. process={"aia_scale_aialev1": None}).
• Supports sequences containing strings, (name, options) tuples, or single-key dicts.
• Gracefully handles the legacy {None: None} workaround pattern without emitting None=None.
• Adds unit tests in drms/tests/test_json.py covering URL query construction for these combinations.
• Adds an end-to-end example (examples/aia_scale_export_request.py) and tutorial documentation in docs/tutorial.rst demonstrating how to request calibrated AIA data.
• Adds a towncrier changelog entry (changelog/122.feature.rst).