Create separate field for disabling rolling updates

[johngmyers]

On further reflection, I think my idea of having rolling updates for an instancegroup be disabled by setting both maxSurge and maxUnavailable to zero is too indirect. This PR makes that behavior be controlled by a new setting.

Fixes #7685
Intended to be backported to 1.18.

[gjtempleton]

/lgtm

I definitely agree with this being explicit rather than implicit.

[johngmyers]

/retest

[johngmyers]

One issue might be naming. It doesn't disable rolling updates entirely, it just disables the drain and terminate behavior. Perhaps DrainAndDelete?

[rdrgmnzs]

After thinking about it I actually like the current naming, I think DrainAndDelete may be even more ambivalent from a users perspective.

[johngmyers]

/retest

[johngmyers]

Let's just check on field naming in Office Hours
/hold

[johngmyers]

/hold cancel

[olemarkus]

/lgtm

[justinsb]

Thanks @johngmyers ... one leftover json field name, but also if we told users to set 0/0, we might not be able to now mark that invalid, and also I think we should probably continue to honor 0/0 as meaning "off", at least for some deprecation period.

[johngmyers]

@justinsb 0/0 hasn't been in a stable release yet, so I think we can skip a deprecation period.

[justinsb]

Ah - that's good news. Fine to disallow 0/0 then :-)

[justinsb]

Thanks @johngmyers - doubly important to get this in so we don't have to deprecate 0/0 :-)

/approve
/lgtm

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