BREAKING CHANGE: incorporated changes planned for v3

[desusai7]

Incorporated changes planned for v3 including breaking changes

List of breaking changes that were taken care as part of this major release are:

1. Converted Credentials class into a data class as shown here, as a result of which this class can no longer be extended and also property currentTimeInMillis is removed from it . Fixed unit tests using CredentialsMock.kt with this change as it can no longer extend Credentials class.
2. Updated the BaseCredentialsManager interface with all the overloads of getCredentials & awaitCredentials methods, and now all the implementing classes should override them instead of defining them directly.
3. Convert await() in the Request.kt here to an abstract function, now all the implementations of it should define the function.

List of other changes that were taken care as part of this major release are:

1. Accepting GsonProvider directly via the internal constructor of DefaultClient as shown here.
2. Disabling logging within DefaultClient by default as shown here.
3. Returning NetworkErrorException directly from the ErrorAdapter's in AuthenticationAPIClient and UsersAPIClient, so now AuthenticationException and ManagementException should just check if the cause is NetworkErrorException to understand if an error is due to Network Error. Created a Util function to check if a throwable is a network error and added unit tests for it.

Testing

This has been tested with all the existing unit tests and with the sample app as well.

• This change adds unit test coverage
• This change adds integration test coverage
• This change has been tested on the latest version of the platform/language

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors