Update gRPC to latest release (#449)

[pingles]

This updates gRPC to 1.34.

[pingles]

Once this is merged I'm going to close #425 and #217. The changes introduced with #433 give operators the ability to mitigate as advised by the gRPC team (along with a default that should reduce impact).

[codecov]

Codecov Report

Merging #451 (19bde8c) into master (600228f) will decrease coverage by 0.50%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #451      +/-   ##
==========================================
- Coverage   55.48%   54.97%   -0.51%     
==========================================
  Files          31       31              
  Lines        1186     1186              
==========================================
- Hits          658      652       -6     
- Misses        465      470       +5     
- Partials       63       64       +1     

Impacted Files	Coverage Δ
pkg/server/tls.go	45.89% <0.00%> (-4.11%)	⬇️