docs: add auth-methods section in acl concepts

[mismithhisler]

Description

Expands on the existing ACL documentation by adding an Auth Method dropdown with sections on JWT and OIDC which contain information related to setting up and debugging both methods.

Most of this added documentation comes from the existing Consul docs, with changes that make sense for Nomad.

Testing & Reproduction steps

Links

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

[EnMod]

New content is showing up fine on the web-presence side, no errors in the build 👍 Deferring to other reviewers for content approval.

[aimeeu]

relates to #24892

[aimeeu]

Thanks @mismithhisler for porting this content over. I took the opportunity to apply style guide rules

[aimeeu]

backport labels - after DM with Michael, for CE, only add 1.9