feat: add model credential schema for Google provider

[fujita-h]

Summary

Fixes #12850

I added the model_credential_schema setting because without it the encrypted key cannot be decrypted.

dify/api/core/provider_manager.py

Lines 891 to 900 in bc3a570

	for variable in model_credential_secret_variables:
	if variable in provider_model_credentials:
	try:
	provider_model_credentials[variable] = encrypter.decrypt_token_with_decoding(
	provider_model_credentials.get(variable),
	self.decoding_rsa_key,
	self.decoding_cipher_rsa,
	)
	except ValueError:
	pass

I don't understand the correct role of model_credential_schema . If this could cause other issues, please fix the PR.

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[kurokobo]

#12850 (comment)

[fujita-h]

I are also creating PR #12853 in another way. Please refer to it.