📖 Add note about clusterctl upgrade test coverage

[sbueringer]

Signed-off-by: Stefan Büringer buringerst@vmware.com

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Part of #8038

[sbueringer]

/assign @fabriziopandini @CecileRobertMichon

[killianmuldoon]

/lgtm
with the updated text

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 175e50dd0856639daf9e31e4f905ad34de39d183

[sbueringer]

@CecileRobertMichon @killianmuldoon @chrischdi @fabriziopandini

We realized that we are actually testing a skip-level upgrade (the one from v1.2 => latest, as v1.2 is a supported release).
We rewrote the note and added a table to make the underlying idea more understandable

(thx @fabriziopandini for pairing on this)

[killianmuldoon]

Suggested change

	Untested upgrade paths are not blocked by clusterctl and should work in general, they are just not tested. Users
	Untested upgrade paths are not blocked by clusterctl but they are just not tested. Users

Nit, but I'm not sure about the grey area of "it should work, but it's not tested". Better IMO just to describe the state.

[sbueringer]

Let's see what others think. I think the assurance that this is something that we expect to work out-of-the-box might be important to users.

[fabriziopandini]

We can keep it as it is, given that the most important part is the next part about users doing their own validation if they want to rely on untested upgrade paths

[fabriziopandini]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 9fbab7d3fa91931e7a3707cde5618f2dcb04eb80

[k8s-ci-robot]

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