Auth: documentation on how to get started is too hard to find

When running apollo locally and calling it with curl or the CLI, no auth stuff is needed.

But if you're connecting a local lightning to your local apollo, you DO need to set up auth.

At the moment the instructions for auth are buried in platform/src/auth/readme.md which is just the worst place. It is linked to from teh readme, so that helps a bit.

But then - the auth docs are full of implementation detail about the hows and whys. The actual "here's how you get set up" bit is lost in a section called "the client CLI", which doesn't feel like the place I'd look for docs on how to configure my local platform.

So basically we need a redo on the docs, with basic setup steps clear and easy to find and follow.

Start with platform/src/auth/readme.md and the README link to understand the current authentication guidance and where users are expected to find it. Reorganize the documentation so local platform authentication setup is clearly surfaced and easy to follow, while keeping implementation details separate; done means a user can readily find the setup steps for connecting local Lightning to local Apollo.