chore(internal/actions): add touch flag to changefinder

[noahdietz]

If there is a need to force a bump/release of all submodules that changed in a previously submitted change, the -touch flag can be used to append a new line to the submodule CHANGES.md file.

This is best used when comparing already submitted changes. For example, a GAPIC generator change touches every gapic module, but the PR doesn't have nested commits for each changed module. The PR is submitted as is, perhaps because it was included with a bunch of other changes or for timing purposes, and the nested commits were not added with changefinder while the PR was open. In this case, we can do the following using changefinder:

1. checkout the merged commit with the target changes: git checkout <some commit has>
2. "save" this to a branch: git checkout -b changed
3. checkout the commit just before the target commit: git checkout <the commit just before>
4. "save" this to a branch : git checkout -b base
5. checkout the changes: git checkout changed
6. generate the nested commits + touch each module:

go run ./internal/actions/cmd/changefinder -q \
  -format=commit \
  -commit-scope=fix \
  -commit-message="describe the change" \
  -touch

7. checkout main, new branch, commit:

git checkout main && \
  git checkout -b bump-modules && \
  git commit -a -m 'chore: bump changed modules' && \
  git push

[quartzmo]

Bravo!!! 🎉

What an excellent PR description! What do you think about adding this stepset to changefinder/README.md? If you're too busy, I'd be happy to do it in a follow-up PR.

[noahdietz]

What do you think about adding this stepset to changefinder/README.md?

Sure thing! Done.