Add logrus hook for sending SkaffoldLogEvents

[MarlonGamez]

Related: #5368

Description
This PR adds an implementation of a logrus.Hook type that will fire off SkaffoldLogEvents whenever we make calls to various logrus.Debug(), logrus.Info(), etc. functions

Follow-up work
Do some tracking of execution state in handler so that we can do some better setting of TaskId and SubtaskId in these events.

[codecov]

Codecov Report

Merging #6250 (bb2d7c6) into master (7453095) will increase coverage by 0.02%.
The diff coverage is 82.85%.

@@            Coverage Diff             @@
##           master    #6250      +/-   ##
==========================================
+ Coverage   70.84%   70.86%   +0.02%     
==========================================
  Files         490      490              
  Lines       22123    22162      +39     
==========================================
+ Hits        15673    15706      +33     
- Misses       5434     5440       +6     
  Partials     1016     1016              

Impacted Files	Coverage Δ
pkg/skaffold/event/v2/logger.go	88.23% <82.35%> (-11.77%)	⬇️
cmd/skaffold/app/cmd/cmd.go	73.65% <100.00%> (+0.14%)	⬆️
pkg/skaffold/server/server.go	47.61% <0.00%> (ø)
...g/skaffold/kubernetes/portforward/entry_manager.go	91.78% <0.00%> (+0.11%)	⬆️
pkg/skaffold/runner/build.go	74.28% <0.00%> (+0.24%)	⬆️
pkg/skaffold/build/cache/retrieve.go	64.40% <0.00%> (+0.30%)	⬆️
pkg/skaffold/kubernetes/status/status_check.go	52.40% <0.00%> (+0.51%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7453095...bb2d7c6. Read the comment docs.

[gsquared94]

what does the level -1 represent?

[MarlonGamez]

this is basically just to avoid marking normal output with a level, since they technically don't have one as they don't come from any logging library. I wasn't sure how to best represent this. I can put it in a variable to make things clear or leave a comment to clarify if you think that's best

[gsquared94]

just a comment should suffice

[gsquared94]

lgtm

[tejal29]

Nice!

{"result":{"timestamp":"2021-07-20T16:34:25.308073Z","skaffoldLogEvent":{"task_id":"","subtask_id":"","level":"DEBUG","message":"Executing template \u0026{envTemplate 0xc001001560 0xc0003d2a40  } with environment map[DISPLAY:/private/tmp/com.apple.launchd.gcpy9xhATO/org.xquartz:0 HOME:/Users/tejaldesai LANG:en_US.UTF-8 LESS:-R LOGNAME:tejaldesai LSCOLORS:Gxfxcxdxbxegedabagacad LaunchInstanceID:C7748237-58DA-4C3E-A5D5-0D8F00A941B5 OLDPWD:/Users/tejaldesai/workspace/skaffold PAGER:less PATH:/Users/tejaldesai/workspace/google-cloud-sdk/bin:/usr/local/opt/[email protected]/bin:/Users/tejaldesai/mdproxy/bin:/Users/tejaldesai/workspace/google-cloud-sdk/bin:/usr/local/opt/[email protected]/bin:/Users/tejaldesai/mdproxy/bin:/usr/local/git/current/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/local/go/bin:/opt/X11/bin:/Library/Apple/usr/bin PWD:/Users/tejaldesai/workspace/skaffold/examples/microservices SECURITYSESSIONID:186ac SHELL:/bin/zsh SHLVL:1 SK_SIGNING_PLUGIN:gnubbyagent SSH_AUTH_SOCK:/private/tmp/com.apple.launchd.8kIonfpvTD/Listeners TERM:xterm-256color TERM_PROGRAM:Apple_Terminal TERM_PROGRAM_VERSION:440 TERM_SESSION_ID:DCB2CB54-F728-4305-8E19-18D0364AC34A TMPDIR:/var/folders/gk/s778hvkj0lb0zl95ywvw0snr00cfc0/T/ USER:tejaldesai XPC_FLAGS:0x0 XPC_SERVICE_NAME:0 ZSH:/Users/tejaldesai/.oh-my-zsh _:/Users/tejaldesai/workspace/skaffold/examples/microservices/../../out/skaffold __CFBundleIdentifier:com.apple.Terminal]"}}}
{"result":{"timestamp":"2021-07-20T16:34:25.308420Z","skaffoldLogEvent":{"task_id":"","subtask_id":"","level":"DEBUG","message":"Found dependencies for dockerfile: [{app.go /go true}]"}}}