Add documentation about using coordinated workers on a service mesh

### Enhancement Proposal

We should create any necessary documentation. Once we've implemented #62, #64, and other related issues the scope of this will be clearer.

Tasks:
* document how to create a custom authorization policy if relating to an on-mesh S3 store via a s3-integrator charm

Start by reviewing issues #62 and #64 and any related implementation issues, since this issue says its documentation scope depends on them. Then locate the project's existing documentation structure. Done means documenting how to create a custom authorization policy for an on-mesh S3 store using an s3-integrator charm.

Written by the indexing model from the issue text.