Add Configuring user authentication guide to navigation

[asteflova]

What changes are you introducing?

Adding a new guide, Configuring User Authentication (https://github.com/theforeman/foreman-documentation/pull/3294), to docs.theforeman.org navigation.

Why are you introducing these changes? (Explanation, links to references, issues, etc.)

N/A

Anything else to add? (Considerations, potential downsides, alternative solutions you have explored, etc.)

N/A

Checklists

• [x] I am okay with my commits getting squashed when you merge this PR.
• [x] I am familiar with the contributing guidelines.

Please cherry-pick my commits into:

• [ ] Foreman 3.12/Katello 4.14 (Satellite 6.16)
• [ ] Foreman 3.11/Katello 4.13
• [ ] Foreman 3.10/Katello 4.12
• [ ] Foreman 3.9/Katello 4.11 (Satellite 6.15; orcharhino 6.8/6.9/6.10)
• [ ] Foreman 3.8/Katello 4.10
• [ ] Foreman 3.7/Katello 4.9 (Satellite 6.14)
• [ ] Foreman 3.6/Katello 4.8
• [ ] Foreman 3.5/Katello 4.7 (Satellite 6.13; orcharhino 6.6/6.7)
• We do not accept PRs for Foreman older than 3.5.

[github-actions[bot]]

The PR preview for f04a66aee7a9392c8de72e4d62b0408d153cede9 is available at theforeman-foreman-documentation-preview-pr-3301.surge.sh

The following output files are affected by this PR:

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[asteflova]

@Lennonka Can you please take a look? I based this on your recent PRs.

The guide itself has been cherry-picked to 3.12, but I'm not requesting the cherry-pick for this PR, again based on your recent PRs to add other guides to navigation.