Add a `websocketCompression` Gateway config field (`'deflate'` by default,
`'none'` to disable) and negotiate `permessage-deflate` on `/api/remote.mux`.
Frames whose JSON text reaches 1024 characters are compressed in the mux send
path, because `ws` ignores its `threshold` option under the default context
takeover. `maxPayload` is bounded by `max(streamInboxBytes, 1 MiB)` so one
compressed frame cannot inflate past the fixed ceiling.
Fixes#6476
imccyu
f881f61024