add plugin for basher

[cornfeedhobo]

Description

This PR seeks to add support for Basher.

Motivation and Context

We don't want to handle installing stuff, and I want a package manager for my bash stuffs (e.g. *env language tools).

Note: to implement full support for Basher, we'll need adjust the load priority of tools it would commonly manage, but after attempting a large PR to address that, I decided that breaking all the changes into separate PRs was a better plan.

How Has This Been Tested?

Locally, and it follows established conventions

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation, I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• If I have added a new file, I also added it to clean_files.txt and formatted it using lint_clean_files.sh.
• I have added tests to cover my changes, and all the new and existing tests pass.

[NoahGorny]

Nice job! Left a couple of comments.

Happy new year 💐

[NoahGorny]

Left you a couple of comments, but be sure I'll use your plugin in my setup soon enough 😄

[NoahGorny]

I will open up the needed issues today