Feature request: `append` mode to add to existing comment

[sparr]

I would like to add content to a comment after each step (or job) of a workflow. Right now I can upsert the content to replace the previous content with the new content, but to implement append I'd need to get the content of the comment myself before manipulating. It would be nice if that functionality was built in.

[tanner-equi]

This would be particularly useful for not destroying the previous message and simply adding "A new _____ is currently running" for things that are commenting back with updated links, etc.

[mmclane]

I love this idea