Add HTTP(S) proxy username and password Setting

[lfu]

What changes are you introducing?

• Add HTTP(S) proxy username setting
• Add HTTP(S) proxy password setting

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

theforeman/foreman#10432

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

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 b9fe65d is available at theforeman-foreman-documentation-preview-pr-3635.surge.sh

The following output files are affected by this PR:

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

show diff

show diff as HTML

[Lennonka]

Small suggestion on the wording of descriptions if you agree

[ekohl]

Why was this merged before the change itself was merged? This needs to be reverted, especially in 3.14.

[aneta-petrova]

Why was this merged before the change itself was merged? This needs to be reverted, especially in 3.14.

#3695

[aneta-petrova]

@lfu Please note that we reverted your change in #3695. Feel free to re-submit it but perhaps it's better to keep the PR in draft state until the corresponding code gets merged?

[Lennonka]

We have a label for pending code: Waiting for code. Please, use it.