Clarify GPG public key extraction process and update keyserver URIs

[lumarel]

I already had twice the issue to make the connection between the gpg --verify Release.gpg Release commands output and the gpg --recv-keys, so this change extends that part.

And recently we noticed, that the receiving from hkp://keyserver.ubuntu.com does not work anymore -> switches this to hkps://

• I am familiar with the contributing guidelines.

Please cherry-pick my commits into:

• Foreman 3.10/Katello 4.12
• Foreman 3.9/Katello 4.11 (Satellite 6.15; orcharhino 6.8)
• Foreman 3.8/Katello 4.10
• Foreman 3.7/Katello 4.9 (Satellite 6.14)
• Foreman 3.6/Katello 4.8
• Foreman 3.5/Katello 4.7 (Satellite 6.13; orcharhino 6.6/6.7)
• Foreman 3.4/Katello 4.6 (EL8 only)
• Foreman 3.3/Katello 4.5 on EL7 & EL8 (Satellite 6.12 on EL8 only; orcharhino 6.4/6.5 on EL8 only)
• We do not accept PRs for Foreman older than 3.3.

[github-actions]

The PR preview for 001bad3 is available at theforeman-foreman-documentation-preview-pr-3024.surge.sh

The following output files are affected by this PR:

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

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show diff as HTML

[maximiliankolb]

Thanks @lumarel I've checked the examples for Debian 11. I'd not add the stdout, but the rest LGTM

[lumarel]

@maximiliankolb Thank you for the help, I think I figured it out 👍🏻

[maximiliankolb]

one small suggestion, rest LGTM.

[maximiliankolb]

Thanks Lukas, LGTM

[maximiliankolb]

Merged to "master" and cherry-picked:
dba651a..bc9fcae 3.10 -> 3.10
9815a98..d3321a3 3.9 -> 3.9