refactor: Use for UserCreationService for idp signup

[joeauyeung]

Stacked on #19201

What does this PR do?

• Adds GOOGLE and SAML to CreationSource
• Uses the UserCreationService when creating new users from those sources

https://www.loom.com/share/7f2dbd9202ed4e8abc4c86a7d6a8f2ea?sid=d3bda613-7f5d-4d69-8cb1-0e6909114249

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• Are there environment variables that should be set?
• What are the minimal test data to have?
• What is expected (happy path) to have (input and output)?
• Any other important info that could help to test that PR

Checklist

• I haven't read the contributing guide
• My code doesn't follow the style guidelines of this project
• I haven't commented my code, particularly in hard-to-understand areas
• I haven't checked if my changes generate no new warnings

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