Archive decommissioned Gitter rooms

[SethTisue]

context: #1256, #1312

[SethTisue]

in the following repos, I put the archive in a comment on an issue:

• Delete and archive Gitter room collection-strawman#577
• Shut down Gitter room, enable GitHub Discussions? scala-xml#526
• Delete and archive the Gitter room community-build#1524

[SethTisue]

here's an archive of the scala/compiler-benchmarks, scala/tooling-contrib, and scala/lsp rooms:

tooling.zip

[SethTisue]

here's an archive of the scala/job-board, scala/center, scala/moocs, and scala/slip rooms:

community.zip

[SethTisue]

and here's scala/contributors, which is the biggest one (besides scala/scala itself):

scala-contributors-messages-2021-12-15.ndjson.zip

[SethTisue]

I haven't included an archive of scala/scala, because it remains open, and also because it would be really big and I'm not sure how big a file we can get away with archiving in the form of comments of GitHub.

This ticket also doesn't include the non-English-language rooms; dealing with that separately at #1318