[feature] Set/get topic schema compatibility strategy

[teabot]

Fixes #783

Motivation

pulsarctl cannot be used to set topic level schema compatibility strategies.

Modifications

Added get/set commands for topic.

Verifying this change

• [x] Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

• I would argue that there should be tests for this and similar functionality, however currently there are none.

Documentation

Check the box below.

Need to update docs?

• [ ] doc-required

• [ ] no-need-doc

• [x] doc

  • Note: These specific commands were erroneously not listed in the Project status section of the README.
  • Added section on differences with pulsar-admin.