feat(languages): add git language under --language flag

[AlejandroSuero]

Is your feature request related to a problem? Please describe.
I am working on a plugin to port freeze as a NeoVim command. When testing it for .git* files, ex. .gitignore|.gitattributes|etc the --language flag says that gitignore|gitattributes|etc filetypes are unknown.

Describe the solution you'd like
To get the --language flag working for git* related filetypes. One way could be to copy bash language into a git language to support on --language.

• rose-pine-moon example from NeoVim:

• freeze .gitignore --config user --theme rose-pine-moon --language bash:
  

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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