Fix broken link for default HTTP proxy

[maximiliankolb]

What changes are you introducing?

fix link in https://docs.theforeman.org/nightly/Managing_Content/index-katello.html#Enabling_Red_Hat_Repositories_content-management

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

• broken: https://docs.theforeman.org/nightly/Installing_Server/index-katello.html#adding-a-default-http-proxy_katello
• fixed: https://docs.theforeman.org/nightly/Installing_Server/index-katello.html#adding-a-default-http-proxy_foreman

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

Also converted to sentence case. Found while reviewing #3545

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 3.13/Katello 4.15 (EL9 only)
• Foreman 3.12/Katello 4.14 (Satellite 6.16)
• Foreman 3.11/Katello 4.13 (orcharhino 6.11 on EL8 only; orcharhino 7.0 on EL8+EL9)
• 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)
• We do not accept PRs for Foreman older than 3.7.

[github-actions]

The PR preview for 0d2b707 is available at theforeman-foreman-documentation-preview-pr-3564.surge.sh

The following output files are affected by this PR:

• Managing_Content/index-katello.html
• Managing_Content/index-orcharhino.html
• Managing_Content/index-satellite.html

show diff

show diff as HTML

[maximiliankolb]

Merged to "master" and cherry-picked:
e55118a..f159955 3.13 -> 3.13
8975474..29c5128 3.12 -> 3.12