feat: Update Alert Configuration Resource

[rakhul-mongo]

Proposed changes

• Added SeverityOverride property to allow overriding default alert severity levels (CRITICAL, ERROR, WARNING)
• Added NotifierId and IntegrationId fields for referencing pre-configured notification integrations
• Updated to latest Atlas SDK (v20250312012)
• Updated examples and test templates to demonstrate the new SeverityOverride field

cfn-testing

Stack Testing

Atlas - Create

Atlas - Update

Atlas - Delete

Jira ticket: CLOUDP-372607

Link to any related issue(s):

Type of change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Manual QA performed:

• cfn invoke for each of CRUDL/cfn test
• Updated resource in example
• Published to AWS private registry
• Used the template in example to create and update a stack in AWS
• Deleted stack to ensure resources are deleted
• Created multiple resources in same stack
• Validated in Atlas UI
• Verified via Atlas REST API
• Tested drift detection
• Included screenshots

Required Checklist:

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• For CFN Resources: I have released my changes in the private registry and proved my change works in Atlas