Show social login options in site credentials login mode

[selanthiraiyan]

Closes #848

Description

The login screen GetStartedViewController doesn't show the social login buttons if enableSiteCredentialsLoginForSelfHostedSites is enabled in configuration.

The social buttons should be displayed if enableSocialLogin is enabled in the configuration. (Irrespective of whether enableSiteCredentialsLoginForSelfHostedSites is true/false)

This PR updates the GetStartedViewController to show the social login options.

Warnings in CI

There are warnings while validating the podspec because a method related to Gravatar image has been deprecated in https://github.com/wordpress-mobile/WordPressUI-iOS/pull/156/

I made an attempt to resolve the warnings.

• I included the Gravatar iOS SDK as a dependency, which requires changing the deployment target from iOS 13.0 to iOS 15.0.
• But changing the deployment target adds other deprecation warnings from iOS. (which makes CI fail again)

For the time being, I used https://github.com/wordpress-mobile/WordPressAuthenticator-iOS/pull/850allow-warningshttps://github.com/wordpress-mobile/WordPressAuthenticator-iOS/pull/850 by Tony, which allows warnings in CI.

Internal discussion about why allow-warnings has been enabled in CI - p1712640270467459/1712574752.341039-slack-CC7L49W13

Before	After

Testing

Please follow the steps from https://github.com/woocommerce/woocommerce-ios/pull/12429 for testing.

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• [x] I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary.

[selanthiraiyan]

Thanks for the review, @itsmeichigo! 🙇 I have addressed your comments. Please feel free to comment if you have further comments.

[itsmeichigo]

All good, please feel free to merge the PR.