tuf/api: Expose tuf.api as a package

[woodruffw]

This just adds tuf/api/__init__.py, turning it into a full package for distribution purposes.

• The code follows the Code Style Guidelines
• [N/A] Tests have been added for the bug fix or new feature
• [N/A] Docs have been added for the bug fix or new feature

[woodruffw]

Amusingly this now breaks the CI, since tuf.api is now correctly discovered and linted 😉

[joshuagl]

According to the pylintrc docs

If the current working directory is in a Python module, Pylint searches up the hierarchy of Python modules until it finds a pylintrc file. This allows you to specify coding standards on a module-by-module basis. Of course, a directory is judged to be a Python module if it contains an __init__.py file.

I think we could add a pylintrc in tuf/api to support the style there?

[lukpueh]

I think we could add a pylintrc in tuf/api to support the style there?

That's actually a really good idea. The linter configuration would need a redo anyway even without style guide change (see in-toto/in-toto#296 (comment), which also applies here). But I'm reluctant to change the default pylintrc as it would require many fixes in code that won't survive the upcoming refactor.

If we create a new config in tuf/api we can use it for new code only and make it the default later. :)

[joshuagl]

I've taken this change to a new PR which also adds a linter for tuf/api #1177