Packit-service: New config option to not comment on PRs at all

[TomasTomecek]

Hey! We're using (and loving) packit in
[osbuild](https://github.com/osbuild/osbuild). We tend to have lots of
back-and-forth on pull requests, force pushing regularly. packit's
notifications add a lot of clutter, both to the discussion and to
notifications.

Honestly, I'd prefer *only* having the status and no comments at all.

_Originally posted by @larskarlitski in https://github.com/packit-service/packit-service/issues/4#issuecomment-527021083_

[TomasTomecek]

Related to #1

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
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[lachmanfrantisek]

We are still waiting for the logs.

[TomasTomecek]

proposal: introduce a new config option:

it would default to true and people would be able to set it to false

true = comment with Congratulations
false = don't comment

[csomh]

How about:

comment:
    pull_request:
        successful_build: false

To allow adding more in the future.

[TomasTomecek]

I mean, I'd love to see something like:

notifications:
    comment:
        pull_request:
            successful_build: false

but yours have only 3 lines, so let's do yours