Simplify GOPATH settings in GH actions

[yurishkuro]

• Add local setup-gopath github action and reuse it in other workflows
  • it writes to $GITHUB_ENV file to expose new env vars to subsequent steps
  • it creates a symlink $GOPATH/src/github.com/uber/jaeger-client-go and exports it as $PROJECT var
• other workflows run this action and the only need to do cd $PROJECT before running Go commands
• fixed the GOPATH issue for #551, but FOSSA fails for other reasons now

[codecov[bot]]

Codecov Report

Merging #552 (6f0b881) into master (4ab51d8) will increase coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   88.53%   88.59%   +0.06%     
==========================================
  Files          61       61              
  Lines        3307     3307              
==========================================
+ Hits         2928     2930       +2     
+ Misses        252      251       -1     
+ Partials      127      126       -1     

Impacted Files	Coverage Δ
utils/reconnecting_udp_conn.go	91.54% <0.00%> (+2.81%)	:arrow_up:

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