Add/update DCO, CoC, contributing ... files

[mmlb]

Description

Update non code files to be uniformish amongst all repos.

Why is this needed

Ensures our repos are all licensed correctly and contain similar/minimum
contribution info files.

[codecov]

Codecov Report

Merging #63 (34a335f) into master (9f5da0a) will increase coverage by 2.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #63      +/-   ##
==========================================
+ Coverage   31.49%   33.49%   +2.00%     
==========================================
  Files           3        3              
  Lines         381      409      +28     
==========================================
+ Hits          120      137      +17     
- Misses        239      249      +10     
- Partials       22       23       +1     

Impacted Files	Coverage Δ
http-server/http_server.go	51.78% <0.00%> (+0.80%)	⬆️
http-server/http_handlers.go	44.50% <0.00%> (+1.48%)	⬆️
grpc-server/grpc_server.go	14.19% <0.00%> (+2.93%)	⬆️

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