Add separate flags for email and Google authentication

[aliasaria]

Introduce separate flags for enabling email and Google authentication. The email authentication options are now conditionally displayed based on the environment variable EMAIL_AUTH_ENABLED. This change ensures that the email UI remains hidden if email authentication is disabled.

[codecov-commenter]

Codecov Report

:x: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
api/transformerlab/routers/auth.py	80.00%	0 Missing and 1 partial :warning:

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