feat: Enable subscriber pool for orb.anchor_linkset queue

[bstasyszyn]

closes #1556

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.02 ⚠️

Comparison is base (74d769f) 88.23% compared to head (6920ba7) 88.21%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1557      +/-   ##
==========================================
- Coverage   88.23%   88.21%   -0.02%     
==========================================
  Files         226      226              
  Lines       21181    21186       +5     
==========================================
+ Hits        18688    18689       +1     
- Misses       1599     1602       +3     
- Partials      894      895       +1     

Impacted Files	Coverage Δ
pkg/anchor/handler/proof/handler.go	90.29% <ø> (ø)
pkg/anchor/vcpubsub/publisher.go	100.00% <ø> (ø)
cmd/orb-server/startcmd/params.go	86.37% <100.00%> (+0.06%)	⬆️
cmd/orb-server/startcmd/start.go	67.52% <100.00%> (ø)
pkg/anchor/vcpubsub/subscriber.go	100.00% <100.00%> (ø)
pkg/anchor/writer/writer.go	88.08% <100.00%> (+0.05%)	⬆️

... and 2 files with indirect coverage changes

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