Init server/scheduler package and use it as proxy for queue & pubsub

[6543]

move towards #6317

this does not change any code flow, it just introduces a new package that will later on combine queue and pubsub coordination.

[woodpecker-bot]

Surge PR preview deployment was removed

[codecov]

Codecov Report

❌ Patch coverage is 6.55738% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.39%. Comparing base (d1c1da1) to head (45d4130).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
server/scheduler/proxy.go	0.00%	26 Missing ⚠️
server/rpc/rpc.go	25.00%	6 Missing ⚠️
server/api/agent.go	28.57%	5 Missing ⚠️
server/scheduler/scheduler.go	0.00%	5 Missing ⚠️
server/api/queue.go	0.00%	4 Missing ⚠️
cmd/server/setup.go	0.00%	3 Missing ⚠️
server/rpc/server.go	0.00%	2 Missing ⚠️
cmd/server/grpc_server.go	0.00%	1 Missing ⚠️
cmd/server/metrics_server.go	0.00%	1 Missing ⚠️
server/api/stream.go	0.00%	1 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6418      +/-   ##
==========================================
- Coverage   35.45%   35.39%   -0.06%     
==========================================
  Files         427      429       +2     
  Lines       28659    28689      +30     
==========================================
- Hits        10160    10155       -5     
- Misses      17569    17603      +34     
- Partials      930      931       +1     

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