v5.4.0-beta.1

See full changelog here.

Commits:

• agent: function to debug agent subscriptions (#834)
• agent: export SubInfo
• Merge branch 'master' into master-ghc9
• server: add env lookups for smp server paths (#817)
• server: add control port commands for clients and ghc threads (#836)
• Merge branch 'master' into master-ghc9
• 5.4.0.1