logpush: modernise methods

Updates the logpush methods to:

- Use the newer client method signatures - Remove the duplicate internal methods
for account/zone level methods in favour of using `*ResourceContainer` - Stop
using `AccessIdentifiers`

This introduces a bit more duplication in the `Create`/`Update` methods however
it does allow us to handle creation and updates separately explicitly instead
of bunching all the logic into a single method with conditionals.