Allow wildcard argument for `--extra`

[apljungquist]

The goal is to make it easy to compile version locks for all runtime dependencies in a way that is robust to human error. By using the wildcard extra the risk of forgetting to list any extra is removed.

Is this a use case pip-tools wants to support? If yes, is the current approach a good one?

Contributor checklist

• [x] Provided the tests for the changes.
• [x] Assure PR title is short, clear, and good to be included in the user-oriented changelog

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