docs(auth): update examples to use modular API

[DoctorJohn]

Description

This PR updates the authentication docs to use the modular API.

I just finished migrating an app to the modular API and put my insights into this PR hoping the next person can benefit from it.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

I'll wait for the Vercel preview and then read the docs again. I already cross-checked the edits I made with my own code after the migration.

🔥

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Name	Status	Preview	Comments	Updated (UTC)
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[github-actions]

Hello 👋, this PR has been opened for more than 2 months with no activity on it.

If you think this is a mistake please comment and ping a maintainer to get this merged ASAP! Thanks for contributing!

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[DoctorJohn]

Hi @mikehardy, IMHO the docs would still benefit from this PR. Thanks in advance for taking a look.

[mikehardy]

Hmmm 🤔 These aren't quite right though...

• currentUser is accessed as auth.currentUser on the return value of getAuth()
• all methods should be patterned as methodName(getAuth(), <params>)

so there should never be an auth import, and there shouldn't be any getAuth().methodName()

The modular sections of the e2e test suites are the working examples at the moment