Add model relative path to CLI commands logs

[lucasdutraf]

Proposed changes:

• Add model relative path to CLI commands logs
  Resolving issue Add model name to the logs in CLI RasaHQ/rasa#6571

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[Henrike100]

I think it would be good to write the changelog.

[Henrike100]

Also, change this:

logger.info("Loading model {}...".format(model_relative_path))

to this:

logger.info(f"Loading model {model_relative_path}...")

[lucasdutraf]

Also, change this:

logger.info("Loading model {}...".format(model_relative_path))

to this:

logger.info(f"Loading model {model_relative_path}...")

Done @Henrike100 ! Thanks for your help! 😄

[arthurTemporim]

Appears good to me :D