Encapsulate handling rotation job register/deregister for plugins

[robmonte]

Description

Adds helper methods for easier development when adding automated root rotation support to plugins.

Also updates AWS secrets to use these new helpers and moves the RotateCredential handler into a separate method.

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.
  • LTS: If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  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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[github-actions]

Build Results:
All builds succeeded! ✅

[github-actions]

CI Results:
All Go tests succeeded! ✅

[kpcraig]

Fields part looks good - aws does too, but I'll let @vinay-gopalan give it a closer look.

[vinay-gopalan]

Looking great! Had some small questions