Include one more level in toc

[adamruzicka]

What changes are you introducing?

Including one more level of heading in TOC.

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

Recently, some heading were pushed to a lower level, making them disappear from the TOC.

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

Extracted from #4809

Contributor checklists

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

Please cherry-pick my commits into:

• Foreman 3.19/Katello 4.21
• Foreman 3.18/Katello 4.20 (Satellite 6.19)
• Foreman 3.17/Katello 4.19
• Foreman 3.16/Katello 4.18 (Satellite 6.18; orcharhino 7.6, 7.7, and 7.8)
• Foreman 3.15/Katello 4.17
• Foreman 3.14/Katello 4.16 (Satellite 6.17; orcharhino 7.4; orcharhino 7.5)
• Foreman 3.13/Katello 4.15 (EL9 only)
• Foreman 3.12/Katello 4.14 (Satellite 6.16; orcharhino 7.2 on EL9 only; orcharhino 7.3)
• We do not accept PRs for Foreman older than 3.12.

[github-actions]

The PR preview for be57fae is available at theforeman-foreman-documentation-preview-pr-4898.surge.sh

No diff compared to the current base

show diff

[Lennonka]

Thank you, Adam, LGTM.

Should we cherry pick this to earlier branches down to 3.16 if we want to have the check on all those branches?
I would prefer to have it on all those branches in case we need to create PRs on them. It doesn't happen that often, we mostly cherry pick from master. But it would be good to have it just in case.

[adamruzicka]

Yes, it should be picked everywhere where we may need the link checking