Update canonicaljson dependency

1.1.2 was a bit broken too :/

1.1.0 and 1.1.1 were broken, so we're updating this to help people make sure
they don't end up on a broken version.

Also, 1.1.0 is speedier...

Merge commit '11d2609d' of https://github.com/matrix-org/synapse into release-v0.27.0

We aren't ready to release this yet, so I'm reverting it for now.

This reverts commit d1679a4e, reversing
changes made to e089100c.

Implement group join API

Add response size metrics

postgres port script: fix state_groups_pkey error

as opposed to join_policy, which is really only pertinent to the
synapse implementation of the group server.

By doing this we keep the group server concept extensible by
allowing arbitrarily complex rules for deciding whether a group
is openly joinable.