Online DDL: ALTER VIEW to respect --postpone-completion strategy flag

[shlomi-noach]

Description

Addresses #11898, see bug description there.

This PR makes ALTER VIEW respect --postpone-completion strategy flag, in a forward migration as well as in a revert migration.

Added endtoend tests to validate.

Related Issue(s)

#11898

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

[vitess-bot]

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[iheanyi]

LGTM 👀

[deepthi]

typo: ALTER is repeated.

[shlomi-noach]

fixed

[shlomi-noach]

Replaced and superseded by #11910, which also handles INSTANT ddl as fast range partition rotation.