Move optional step about DHCP to Integrating Provisioning Infrastructure Services guide

[aneta-petrova]

[...] this is a really niche bit of procedure. It only affects the DHCP integration so should it become part of https://docs.theforeman.org/3.16/Integrating_Provisioning_Infrastructure_Services/index-katello.html#configuring-dhcp-integration where we tell users to enable DHCP? I'm not sure that running it at this point (the user hasn't installed the server yet) even works.

Originally posted by @ekohl in #4210 (comment)