feat(prune): add `--use-gitignore` flag (#9797)
### Description
Closes #9789
Adds a flag for opting out of respecting `.gitignore`. If you want to
copy over files that are ignored by `git` you can now pass
`--use-gitignore=false` to `turbo prune`.
### Testing Instructions
Added unit tests. Quick manual test:
```
# A gitignored file in the app
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ stat apps/web/.turbo
16777234 160702923 drwxr-xr-x 6 olszewski wheel 0 192 "Jan 24 14:05:04 2025" "Jan 24 14:05:04 2025" "Jan 24 14:05:04 2025" "Jan 24 14:05:04 2025" 4096 0 0 .turbo
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ turbo_dev --skip-infer prune web --use-gitignore=false
turbo 2.3.4
Generating pruned monorepo for web in /private/tmp/turborepo-gitignore-bug/out
- Added @repo/eslint-config
- Added @repo/typescript-config
- Added @repo/ui
- Added web
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ stat out/apps/web/.turbo/
16777234 160756779 drwxr-xr-x 3 olszewski wheel 0 96 "Jan 24 14:07:47 2025" "Jan 24 14:07:30 2025" "Jan 24 14:07:30 2025" "Jan 24 14:07:30 2025" 4096 0 0 out/apps/web/.turbo/
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ rm -r out
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ turbo_dev --skip-infer prune web --use-gitignore
turbo 2.3.4
Generating pruned monorepo for web in /private/tmp/turborepo-gitignore-bug/out
- Added @repo/eslint-config
- Added @repo/typescript-config
- Added @repo/ui
- Added web
[0 olszewski@chriss-mbp] /tmp/turborepo-gitignore-bug $ stat out/apps/web/.turbo/
stat: out/apps/web/.turbo/: stat: No such file or directory
```
