BED-5013: Deprecate Create SAML Endpoint

[iustinum]

Description

This PR adds a new SSO endpoint POST /api/v2/sso-providers/saml to replace the existing POST /api/v2/saml/providers endpoint. The old endpoint is marked as deprecated, and OpenAPI documentation is updated accordingly.

Motivation and Context

This PR addresses: BED-5013

By migrating to the new endpoint, we standardize SSO provider interactions and guide users away from the soon-to-be-removed SAML-specific endpoints.

How Has This Been Tested?

• Verified endpoint functionality through existing integration tests.
• Confirmed that both old and new endpoints return expected responses.
• Reviewed documentation and ensured it reflects the new endpoint and deprecation notice.

Screenshots (optional):

Types of changes

• Chore (a change that does not modify the application functionality)

Checklist:

• I have met the contributing prerequisites
  • Assigned myself to this PR
  • Added the appropriate labels
  • Associated an issue: Issues and Pull Requests README #672
  • Read the Contributing guide: https://github.com/SpecterOps/BloodHound/wiki/Contributing
• I have ensured that related documentation is up-to-date
  • Open API docs
  • Code comments (GoDocs / JSDocs)
• I have followed proper test practices
  • Added/updated tests to cover my changes
  • All new and existing tests passed

[mistahj67]

Code LGTM and locally tested