Manually trigger external command by writing comment

Is it somehow possible to make Gitea execute an external command when a user writes a certain “command” as comment?

In my specific case I’d like to trigger a build on my build server when I write a comment on a pull request, e.g.:

@BuildBot Build!

Of course I could configure my build server to periodically query if there are any new commits; or I could use webhooks – but I am explicitly searching for some manual action which can be triggered from within Gitea. Also a “Build now” button for each PR would do which performs e.g. a HTTP POST.