Adding `Auth0.AuthenticationApi` package dependency

[kailash-b]

Description

• Adds Auth0.AuthenticationApi package as a direct dependency.
• Developers can now use the features of Auth0.AuthenticationApi without adding/managing a separate reference.
• Examples are updated to show how to register the dependency and use the AuthenticationApiClient.

Internal References

• SDK-5567
• Discovery

Testing

• Tested the changes on the sample application as well.
• [x] This change adds test coverage for new/changed/fixed functionality

Checklist

• [x] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not main