Add page about kube-context handling in docs concepts section

[corneliusweig]

Relates to #2510 and #2447
Also see https://github.com/GoogleContainerTools/skaffold/blob/master/docs/design_proposals/configurable-kubecontext.md

Description

This PR adds a page to the concepts section in the docs about the kube-context activation. The PR also addresses a comment from #2510 (review).

User facing changes
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Before
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After
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Next PRs.
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Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Mentions any output changes.
• Adds documentation as needed: user docs, YAML reference, CLI reference.
• Adds integration tests if needed.

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

[codecov]

Codecov Report

Merging #2992 into master will increase coverage by 0.07%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
pkg/skaffold/build/custom/custom.go	62.5% <0%> (-1.44%)	⬇️
pkg/skaffold/runner/diagnose.go	12.67% <0%> (-0.76%)	⬇️
pkg/skaffold/kubernetes/context/context.go	100% <0%> (ø)	⬆️
pkg/skaffold/build/misc/graceful.go	66.66% <0%> (ø)
pkg/skaffold/kubernetes/status_check.go	77.77% <0%> (ø)
pkg/skaffold/schema/profiles.go	88.5% <0%> (+0.06%)	⬆️
pkg/skaffold/schema/defaults/defaults.go	92% <0%> (+0.91%)	⬆️
pkg/skaffold/build/gcb/types.go	16.12% <0%> (+1.42%)	⬆️
pkg/skaffold/docker/dependencies.go	73.91% <0%> (+2.17%)	⬆️
pkg/skaffold/build/custom/dependencies.go	83.33% <0%> (+8.33%)	⬆️

[corneliusweig]

cc @balopat as you raised this in #2510 (review)

[container-tools-bot]

Please visit http://35.236.111.216:1313 to view changes to the docs.

[tejal29]

Suggested change

	By default, Skaffold uses the _current_ kube-context from your kube-config file.
	By default, Skaffold uses the _current_ kube-context from your kube-config file at `~/.kube/config`

[corneliusweig]

I also thought about including this, but Skaffold also respects the KUBECONFIG env var. So the location you suggest isn't always correct. I'm fine either way, but please just confirm that you really want the path there.

[nkubala]

I think we should leave the path out, since this file doesn't necessarily have to live anywhere.

[tejal29]

Suggested change

	1. Via the `kube-context` flag
	1. `kube-context` flag

[tejal29]

you could re-word this as

Suggested change

	It is illegal to activate both profiles which happens when
	Activating multiple `kube-contexts` will result in error.

You could also mention the error we print here.

[corneliusweig]

That wording sounds as if it is illegal to have multiple differing profiles.deploy.kubeContext configurations. However that is not the case.
What I am trying to say is that it is illegal to have automatic profile activations via a matching kube-context AND the effective kube-context changes.

I'll try to make that point clearer.

[tejal29]

This is a little bit confusing.
You could say,

Suggested change

	The kube-context has a double role for Skaffold profiles:
	Multiple `kube-contexts` can be activated from skaffold profiles.

[corneliusweig]

A put some thoughts into this, if I can make this whole part clearer. Can you have another look?

[nkubala]

I think this makes sense. the main point here is that the kube-context has two semantic roles in the activation of skaffold profiles, but not that multiple contexts can be activated from profiles (since that's not really true).

[corneliusweig]

Hey @tejal29, thanks for doing such a thorough check of this docs change. I tried to improve the readability and logic flow. Can you take another look?

[corneliusweig]

That CI failure seems unrelated.

[nkubala]

LGTM, thanks for clarifying this @corneliusweig

addressed