Add deprecation warning for ACD plugin

[maximiliankolb]

What changes are you introducing?

Foreman 3.17 does not support foreman_acd and smart_proxy_acd.

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

follow-up to #4359 (Remove docs for foreman_acd from nightly)

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

Note that the package is currently still present on https://yum.theforeman.org/plugins/nightly/el9/x86_64/.

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.

[maximiliankolb]

draft PR until I know how this actually works.

[github-actions]

The PR preview for 714d092 is available at theforeman-foreman-documentation-preview-pr-4420.surge.sh

The following output files are affected by this PR:

• Release_Notes/index-foreman-deb.html
• Release_Notes/index-foreman-el.html
• Release_Notes/index-katello.html
• Release_Notes/index-orcharhino.html
• Release_Notes/index-satellite.html

show diff

show diff as HTML

[maximiliankolb]

Refs ATIX-AG/foreman_acd#50