Add support for reloading raft config

[ncabatoff]

Description

SIGHUP now reloads the raft configuration given in the storage stanza that is reloadable. sys/config/state/sanitized now includes the storage stanza settings.

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]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[mpalmi]

I left some high-level comments and clarifying questions. I think this looks great and am personally excited to see this patch. Just want to make sure we're not overlooking some edge-cases.

[mpalmi]

LGTM!