feat(anta)!: Add support for path to custom tests

[titom73]

Add ability to load user's defined tests using ANTA catalog loader (Issue #118 )

Now, catalog uses python module name to target correct tests:

---
anta.tests.software:
  - verify_eos_version:
      versions: 
        - 4.25.4M
        - 4.26.1F
anta.tests.routing:
  generic:
    - verify_routing_protocol_model:
        model: multi-agent

First level has to use full module name and then, loader do recursive search within this module to find correct submodules and tests

Breaking changes

• Catalog format must use anta.tests.<test module> and not just <test module>

Todo

• Validate behaviour with external test library
• Update documentation for catalog
• Document how to create custom tests lib

[ksator]

LGTM