feat(fips): return an error when creating a kerberos client

[kruskall]

Proposed commit message

return an error when creating a kerberos client in fips mode

Checklist

• My code follows the style guidelines of this project
• 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.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

related to #42867

Use cases

Screenshots

Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @kruskall? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[simitt]

Changes look good to me as part of #42867. However, in addition to returning an error when creating the Kerberos client, the beats should not expose and support any Kerberos related configuration in the first place.

@kruskall are you planning on tackling this as follow up work? (please see the sub issues in #42867).

[kruskall]

I'll open a PR for the configuration separately