find_issue.R functionalized and added to ottrpal

[cansavvy]

find_issue.R needs to be functionalized and added to the ottrpal package (along with a unit test).

Currently it is called by the check-urls.yml action (Periodic URL checker -- the one that runs when no PRs are filed, but just every so often).

It is currently called like this:

Rscript --vanilla find_issue.R --repo $GITHUB_REPOSITORY --git_pat $GH_PAT

It's arguments need to be a repository, a credential for GH_PAT, and also we should probably make it more flexible for other purposes. So currently it's hard coded that it will look for text in the title that is 'Broken URLs found in the course!' but let's make this an argument so that people can specify what kind of title they are looking for.