Identity first-time contributors and external contributors

[pjcozzi]

We like to tweet to congratulate and thank first-time contributors and external contributors. It would be useful for a comment to explicitly @mention the outreach team so they know to tweet.

Currently, it is possible to identify first-time contributors by filtering emails for "Welcome to the Cesium community", but I don't know if there is a unique way to filter for external contributors, but this would be easy for the concierge to check.

CC @slchow @vanessamoore

[pjcozzi]

Bumping this since we like to tweet about all community contributions.

When a pull request from a community contributor is merged, the concierge could just @ mention someone(s) (configurable) and also say if it is a first time contributor.

Longer-term, if/when the concierge can label issues, it could label issues as "community contribution", "first-time contributor", etc. - which would be useful for stats as well.

[pjcozzi]

@OmarShehata is this one on the short-term radar?

[OmarShehata]

Yes, I ran into the same problem of checking the correct branch/fork as in this PR #118 so it'll be easy to do right after that one.

[OmarShehata]

This is merged, and I have seen concierge reporting "Thanks for your first time contribution!" need to investigate why it didn't post for this one CesiumGS/cesium#7944.

[verybigzhouhai]

@OmarShehata Is it because the first PR I submitted before was shut down by myself, so it was not identified this time? CesiumGS/cesium#7911 ,When I shut down the pr, I received a message from the concierge.

[OmarShehata]

I think it may be an error in my logic, that Concierge checks the branch you're merging into to see if your name is in the contributors.md, and decides based on that whether you're a new contributor.

But I think what happened here, is that since Concierge checks after the PR is merged, then your name is already in contributors.md in master, so it doesn't post. I think I need to check for the commit when the PR was opened, not when the PR is merged.