feat: add health check server

[kevmo314]

Description

This change adds a grpc health check service to the signalling server.

[codecov]

Codecov Report

Merging #589 (c9d2992) into master (0e3628e) will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #589      +/-   ##
==========================================
- Coverage   36.20%   36.05%   -0.16%     
==========================================
  Files          25       25              
  Lines        2646     2646              
==========================================
- Hits          958      954       -4     
- Misses       1556     1559       +3     
- Partials      132      133       +1     

Impacted Files	Coverage Δ
pkg/sfu/subscriber.go	57.69% <0.00%> (-1.29%)	⬇️
pkg/sfu/router.go	46.19% <0.00%> (-1.17%)	⬇️

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[adwpc]

LGTM