🌱 Ensure BMH name is a valid DNS label

[nerok]

What this PR does / why we need it:
We don't want anyone to create a BMH with a name which isn't a compliant DNS hostname, that will cause issues.

Which issue(s) this PR fixes:
Fixes parts of #855

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[zaneb]

There is more to validating a DNS name than this; e.g. it cannot start or end with a -, should be no more than 63 characters.

I suggest calling this function to validate it.

[nerok]

Changed to that function now, some tests needed changes, and otherwise I added (maybe too many) tests to validate that we check what we think we check.

[tuminoid]

/ok-to-test

[tuminoid]

/lgtm
/cc @dtantsur @zaneb

Btw, can we break existing installations by validating and failing this now, or did we have some other runtime check doing the same?

[zaneb]

Btw, can we break existing installations by validating and failing this now, or did we have some other runtime check doing the same?

CR names are actually already validated against IsDNS1123Subdomain(). And we already forbid .. So the only actual change is limiting the length to 63 I think?

Ideally we would only call this from ValidateCreate() though, so it would only affects new BMHs, not existing ones.
validateHost() is called from validateChanges() as well.

[nerok]

Should the length check be moved to ValidateCreate then, so it isn't ran on changes? Or should validateChanges pick that error out and rather log it? Those are the alternatives I could come up with

[zaneb]

I think moving it to validateCreate makes sense

[nerok]

It got a lot more complicated to ignore or reimplement the validations, so I think this solution was simple enough.

[tuminoid]

/lgtm
/cc @zaneb

[MahnoorAsghar]

(LGTM)