Task: change developer documentation, names in the code and targets to artifacts

[MVrachev]

What is the task about?

We should consider renaming all places where we refer to target files from targets to artifacts.
This way it will be easier to understand from new contributors, we will remove the possibility of a developer mistaking targets - the role for targets - multiple artifacts.

Two examples:

• repository-service-tuf-cli/repository_service_tuf/helpers/cli.py

  Line 45 in 980495a

  publish_targets: bool = True

• here https://github.com/kairoaraujo/repository-service-tuf-cli/blob/4d92647e388a496fda5cce45abc5cf707850b200/repository_service_tuf/helpers/api_client.py#L161

Code of Conduct

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