Migrate devtools wiki & update old flutter wiki links (#7875)
Part of https://github.com/flutter/flutter/issues/145009
This migrates the home and triage page of the devtools wiki into checked in files, and updates all old references to flutter/flutter/wiki
I'll update the original wiki pages to point to these new places after this lands
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[build.yaml badge]: https://github.com/flutter/devtools/actions/workflows/build.yaml/badge.svg
