add flag sync-remote-cache

[gsquared94]

Fixes: #6145

Description

This PR implements a flag sync-remote-cache which has three values

	// clone missing repositories and sync them on each skaffold run
	always = "always"
	// clone missing repositories but do not sync found repositories
	missing = "missing"
	// do not clone missing repositories, and do not sync found repositories
	never = "never"

This flag allows users to turn off syncing their remote modules on every run of skaffold.
It supersedes the value set in the config.

[codecov]

Codecov Report

Merging #6210 (c258038) into master (67d8c45) will decrease coverage by 0.28%.
The diff coverage is 76.31%.

@@            Coverage Diff             @@
##           master    #6210      +/-   ##
==========================================
- Coverage   71.16%   70.88%   -0.29%     
==========================================
  Files         481      489       +8     
  Lines       21762    22086     +324     
==========================================
+ Hits        15488    15655     +167     
- Misses       5284     5425     +141     
- Partials      990     1006      +16     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	90.81% <ø> (ø)
pkg/skaffold/config/options.go	100.00% <ø> (ø)
pkg/skaffold/config/repo_cache.go	59.09% <59.09%> (ø)
pkg/skaffold/git/errors.go	100.00% <100.00%> (ø)
pkg/skaffold/git/gitutil.go	69.23% <100.00%> (+1.41%)	⬆️
pkg/skaffold/log/stream/stream.go	0.00% <0.00%> (-25.00%)	⬇️
pkg/skaffold/kubernetes/logger/log.go	32.53% <0.00%> (-10.84%)	⬇️
pkg/skaffold/docker/image.go	69.93% <0.00%> (-10.16%)	⬇️
pkg/skaffold/build/builder_mux.go	37.70% <0.00%> (-8.30%)	⬇️
pkg/skaffold/sync/sync.go	65.77% <0.00%> (-7.44%)	⬇️
... and 24 more

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[briandealwis]

Minor tweaks