Add getIdToken method

[mchr3k]

Explain your changes

I've raised a support thread in Discord: https://discord.com/channels/1070212618549219328/1179456563627438141

[...]can you help me understand how to use and validate the ID Token (https://kinde.com/docs/build/about-id-tokens/) ? I'm already passing the Access Token to my REST API through the "authorization" HTTP header. However, this token doesn't contain the user's email address (https://kinde.com/docs/build/about-access-tokens/) and so on every REST API call I'm currently getting a M2M token and calling the Kinde API to get the user object to get their email address. The ID token includes the user's email address (https://kinde.com/docs/build/about-id-tokens/) but I can't see any example in your docs of the recommended way of passing this token through to a REST API and validate serverside that the ID token is valid.

This PR exposes a new getIdToken() method which returns the complete ID Token: https://kinde.com/docs/build/about-id-tokens/

Checklist

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[DaveOrDead]

Hey @mchr3k thanks for this :)

Just checking if this PR is still needed or did the additional claims feature solve your use case?