Add option to wait for connection to /v2/events on gRPC/HTTP server

[MarlonGamez]

Description
This PR adds the option for the user to have skaffold pause execution on initialization of the gRPC/HTTP server. Execution will continue when a request to /v2/events is made. This will help ensure that users of the server can connect before Skaffold execution ends early in some cases.

This PR also moves the call to event.SendErrorMessageOnce to the server shutdown callback function, which ensures that the error message gets sent out before the server is shut down.

[codecov]

Codecov Report

Merging #6545 (712b7dc) into main (cfe7882) will increase coverage by 0.08%.
The diff coverage is 44.44%.

@@            Coverage Diff             @@
##             main    #6545      +/-   ##
==========================================
+ Coverage   70.44%   70.52%   +0.08%     
==========================================
  Files         515      515              
  Lines       23144    23152       +8     
==========================================
+ Hits        16303    16328      +25     
+ Misses       5785     5770      -15     
+ Partials     1056     1054       -2     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/cmd.go	70.68% <0.00%> (-0.38%)	⬇️
cmd/skaffold/app/cmd/flags.go	90.81% <ø> (ø)
cmd/skaffold/skaffold.go	0.00% <ø> (ø)
pkg/skaffold/config/options.go	100.00% <ø> (ø)
pkg/skaffold/server/server.go	46.87% <0.00%> (-0.75%)	⬇️
pkg/skaffold/event/v2/event.go	84.22% <66.66%> (-0.37%)	⬇️
pkg/skaffold/build/ko/builder.go	100.00% <0.00%> (ø)
pkg/skaffold/build/jib/jib.go	73.50% <0.00%> (+0.66%)	⬆️
pkg/skaffold/docker/parse.go	88.23% <0.00%> (+0.84%)	⬆️
pkg/skaffold/output/color.go	100.00% <0.00%> (+3.70%)	⬆️
... and 4 more

---

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 cfe7882...712b7dc. Read the comment docs.

[aaron-prindle]

LGTM, seems this flag could be defined on more commands and it looks like a commented out line was left (see comments)