Add Hammer reference to navigation

[Lennonka]

What changes are you introducing?

Adding #4220 to upstream navigation in Nightly and 3.16

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

Follows up on #4220

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

• Split off Hammer reference into separate guide #4220 has to be merged first
• Does this have to be cherry picked in order to appear in 3.16 or not?

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 3.16/Katello 4.18 (Satellite 6.18)
• Foreman 3.15/Katello 4.17
• Foreman 3.14/Katello 4.16 (Satellite 6.17; orcharhino 7.4)
• 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)
• Foreman 3.11/Katello 4.13 (orcharhino 6.11 on EL8 only; orcharhino 7.0 on EL8+EL9; orcharhino 7.1 with Leapp)
• Foreman 3.10/Katello 4.12
• Foreman 3.9/Katello 4.11 (Satellite 6.15; orcharhino 6.8/6.9/6.10)
• We do not accept PRs for Foreman older than 3.9.

[github-actions]

The PR preview for dbf466c is available at theforeman-foreman-documentation-preview-pr-4222.surge.sh

No diff compared to the current base

show diff

[maximiliankolb]

diff looks reasonable to me