db: consider possibility of NextVaultRotation being unset on queue population (VAULT-35639)

[elliesterner]

Description

NextVaultRotation was introduced to the static role struct in Vault 1.15.0. In 1.19.0, vault changed to use this field to determine when to enqueue roles for rotation here. However, if a static role was originally created on a version older than 1.15.0, it won’t have a NextVaultRotation value set. After upgrading to 1.19.0 or above, vault sees this value as the zero value (time.Time{}) and rotates the cred immediately.

TODO only if you're a HashiCorp employee

• Backport Labels: If this fix needs to be backported, use the appropriate backport/ label that matches the desired release branch. Note that in the CE repo, the latest release branch will look like backport/x.x.x, but older release branches will be backport/ent/x.x.x+ent.
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  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[github-actions]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[benashz]

A few more suggestions/comments for you, otherwise this PR is looking good!

[benashz]

LGTM!