See https://github.com/matrix-org/synapse/issues/13375

Use attached image
Fix changes key
Missing stage
Fix tags for ci builds
Make lint
Use branch pipelines
Fix changes rule
Fix needs
Exit success after docker build
Try to fix postgres lockfile
Whitelist var run in container build
Make tests homeserver name generic

I think I finally worked out the issues w/ linking against the
nlohmann JSON library.  I have updated the build and the various
CI scripts.