docs(auth): provide auth DI tokens documentation

[KingDarBoja]

Checklist

• Issue number for this PR: Docs request: Document all DI tokens with example usage #2663
• Docs included?: yes
• Test units included?: no
• In a clean directory, yarn install, yarn test run successfully? yes

Description

Updating the Auth documentation with the usage of DI tokens 🚀

[jamesdaniels]

Thanks! Looks good.

[conde2]

@KingDarBoja Is is possible to dynamic change the language code ?

I have an async operation to fetch the language code from local storage, and I couldn't find a way to inject it async.

I've tried this, with no success

    this.angularFireAuth.languageCode = new Promise<string>(( resolve ) => {
      resolve("fr");
    });

My solution was do this:

(await this.angularFireAuth.app).auth().languageCode = language;