[8.18](backport #4542) pbkdf2 settings validation is FIPS compliant

[mergify]

What is the problem this PR solves?

User pbkdf2 settings are not validated for FIPS compliance.

How does this PR solve the problem?

Validate pbkdf2 settings.

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

  ---

  This is an automatic backport of pull request pbkdf2 settings validation is FIPS compliant #4542 done by Mergify.

[mergify]

Cherry-pick of 63b6b92 has failed:

On branch mergify/bp/8.18/pr-4542
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit 63b6b92.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   changelog/fragments/1741108238-pbkdf2-settings-is-FIPS-compliant.yaml

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   internal/pkg/config/pbkdf2.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elastic-sonarqube]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 40%)

See analysis details on SonarQube