Support other top-level gitignore locations

[rshin]

Is your feature request related to a problem? Please describe.
Pants uses patterns in the .gitignore to find additional files to ignore: https://www.pantsbuild.org/docs/reference-global#section-pants-ignore-use-gitignore

However, Git itself also looks at $GIT_DIR/info/exclude (usually .git/info/exclude) and $XDG_CONFIG_DIR/git/ignore (usually ~/.config/git/ignore, unless core.excludeFiles in ~/.gitconfig is set differently) to get additional ignore patterns: https://git-scm.com/docs/gitignore.

Describe the solution you'd like
It would be good if Pants supported these locations too.

This request is similar to #5682 but potentially simpler, as the interpretation of the patterns in these other ignore files is the same (they are relative to the repository root rather than some other location) and there is a fixed number of them.

Describe alternatives you've considered
You can replicate the additional ignore patterns in .pants.rc

[Eric-Arellano]

Great idea! I added this to the Onboarding project and label. Fixing this means it's more likely Pants will Just Work on a new repo, which is an important goal for Pantsbuild.

[Eric-Arellano]

Would you have any interest in implementing this? We'd be happy to try to scope out how this would work. It would involve writing some Rust code.

[sureshjoshi]

Semi-relevant Slack thread example today:
https://pantsbuild.slack.com/archives/C046T6T9U/p1663933840682049

Summary: Bastian changed his pants_ignore which caused the .git to be picked up (because the default pants_ignore was overwritten) and caused test restarts due to filesystem changes in the now-watched git folder. Solution was to use pants_ignore.add instead.

However, when using this set of ignores:

pants_ignore.add = [
  "/apps/",
  "/src/bin",
  "/src/docker",
  "/frontend/",
  "/python/",
  ".idea/",
  "*.md",
]

This was popping up in the log: [INFO] notify invalidation: cleared 0 and dirtied 0 nodes for: {"pants-TODOS.md~"}

Because the tilde temp file wasn't in the .gitignore or pants_ignore anywhere.

On my machine, all of these temp files are excluded directly from my ~/.gitignore_global (same for .DS_Store files). I never really clued into why I was getting restarts in some of my tests or packages, but typically when they're going on, I stop saving any files in my working dir. I now think they might be caused by temp files being picked up sometimes by accident.

[Eric-Arellano]

You were right that this indeed was more tractable than #5682. Thanks again for the suggestion!

See #18649.