feat(gcf-utils): export a function for the comment mark (#1173)
feat(gcf-utils): export a function for the comment mark (#1173)

fixes #1160

Now a bot can utilize the following two functions for adding an issue
comment and providing a checkbox for refreshing the comment.

- addOrUpdateIssueComment
- getCommentMark

snippet-bot has an example implementation.

Co-authored-by: Justin Beckwith <0b357449eb5b1ce3bad523b6be0681e856776d8e@gmail.com>
googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots,googleapis/repo-automation-bots