[8.x](backport #4182) Redact static tokens and custom http headers

[mergify]

What is the problem this PR solves?

Static tokens and (potentially) custom http headers can expose secrets in diagnostic bundles.

How does this PR solve the problem?

Redact sensitive values within the Config.Redact() call,

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.

  ---

  This is an automatic backport of pull request Redact static tokens and custom http headers #4182 done by Mergify.

[mergify]

Cherry-pick of d0993e8 has failed:

On branch mergify/bp/8.x/pr-4182
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit d0993e86.
  (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:
	modified:   internal/pkg/config/config_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/pkg/config/config.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

[mergify]

This pull request has not been merged yet. Could you please review and merge it @michel-laterman? 🙏

[pkoutsovasilis]

@michel-laterman just cc'ing for the CI failures 🙂

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube