VAULT-31409: trace unsealInternal function

[bosouza]

Description

This PR adds the environment variable VAULT_ENABLE_UNSEAL_TRACE that when enabled will cause Vault to write a Go trace file to the /tmp directory, like /tmp/trace_unsealInternal_2024-11-13T12:06:13-03:00. This file can be inspected using the go tool trace command and will help us debug cases where the unseal operation takes too long.

Jira: VAULT-31409

TODO only if you're a HashiCorp employee

• Backport Labels: If this PR is in the ENT repo and needs to be backported, backport
  to N, N-1, and N-2, using the backport/ent/x.x.x+ent labels. If this PR is in the CE repo, you should only backport to N, using the backport/x.x.x label, not the enterprise labels.
  • 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.
• Jira: If this change has an associated Jira, it's referenced either
  in the PR description, commit message, or branch name.
• RFC: If this change has an associated RFC, please link it in the description.
• ENT PR: If this change has an associated ENT PR, please link it in the
  description. Also, make sure the changelog is in this PR, not in your ENT PR.

[github-actions]

CI Results: failed ❌
Failures:

Test Type	Package	Test	Logs
standard	command/server	TestConfig_Sanitized	view test results
standard	http	TestSysConfigState_Sanitized	view test results
standard	http	TestSysConfigState_Sanitized/inmem_storage,_no_HA_storage	view test results
standard	http	TestSysConfigState_Sanitized/inmem_storage,_raft_HA_storage	view test results
standard	http	TestSysConfigState_Sanitized/raft_storage	view test results

[bosouza]

still want to make this more similar to VAULT_STACKTRACE_WRITE_TO_FILE for the sake of consistency