Add input parameter filter for git commands

[emcfarlane]

This adds a new input parameter filter to assist in working with large git projects. The param filter sets the git filter-spec argument when fetching repositories. Only one argument can be provided, the combined form can be used to set multiple filters. When using filter combined with a subdir the checkout will now also be sparse to further reduce the number of workspace files.

The documentation for filter arguments can be found in the git rev-list command: https://git-scm.com/docs/git-rev-list#Documentation/git-rev-list.txt---filterltfilter-specgt
See this blog post on the different filter checkouts that may be used: https://github.blog/open-source/git/get-up-to-speed-with-partial-clone-and-shallow-clone/

As an example using the envoy project as a larger repository, it can be built using the new filter argument:

 buf build https://github.com/envoyproxy/envoy.git#subdir=api,branch=main,filter=tree:0

Which reduces the fetch of the git repository from 10.6s to 2.6s.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jan 16, 2025, 6:14 PM

[bufdev]

Make sure you update docs too