Add flag to save events to a file

[priyawadhwa]

Adds the --event-log-file flag, which when set to a filepath will save Skaffold events to a file when --enable-rpc is also enabled.

This will make it easier to collect data around performance metrics for the performance dashboards. We can just parse the events in the file after skaffold executes, and figure out how long each stage took.

[MarlonGamez]

This looks good, It looks like jsonpb is deprecated in favor of protojson though

[priyawadhwa]

Yah I noticed that too -- unfortunately it isn't as simple as just changing the name of the import, since it looks like the upgrade isn't backwards compatible. Replacing with protojson fails with this compiler error:

cannot use &logEntry (value of type *proto.LogEntry) as protoreflect.ProtoMessage value in argument to protojson.Unmarshal: missing method ProtoReflect

I think if we want the upgraded library to work we also have to recreate our proto file with a new version of protoc-gen-go built from the new library. This would require:

• Changing all of our files that require jsonpb to use protojson (not too hard)
• Changing the Dockerfile used for upgrading/testing the proto to use protojson and upgrade protoc-gen-go to match (feel like this is trickier than it sounds)
• Making sure the newly generated proto is backwards compatible with existing users/IDEs

Until we do that big upgrade, I think we have to keep using the deprecated version :/ I guess I'll have to see if there's a way around it for the unit test.

[codecov]

Codecov Report

Merging #5125 (d61ca86) into master (53a81ad) will decrease coverage by 0.00%.
The diff coverage is 41.17%.

@@            Coverage Diff             @@
##           master    #5125      +/-   ##
==========================================
- Coverage   72.14%   72.13%   -0.01%     
==========================================
  Files         381      381              
  Lines       13474    13491      +17     
==========================================
+ Hits         9721     9732      +11     
- Misses       3042     3046       +4     
- Partials      711      713       +2     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	82.85% <ø> (ø)
pkg/skaffold/config/options.go	100.00% <ø> (ø)
pkg/skaffold/server/server.go	43.56% <0.00%> (-1.80%)	⬇️
pkg/skaffold/event/event.go	90.76% <53.84%> (-1.15%)	⬇️
pkg/skaffold/util/tar.go	56.00% <0.00%> (+5.33%)	⬆️

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[MarlonGamez]

LGTM! Thanks for clarifying the proto situation 👍🏼