Fixes #37189 - Registration before & after snippets

[stejskalleos]

before_registration & after_registration snippets allow users to add their code to the template without directly editing it.

[nofaralfasi]

LGTM.
I also suggest adding it to the documentation.

[maximiliankolb]

Hey @stejskalleos

I like the idea as previously expressed during discussions/reviews in foreman-documentation. However, why did you go with these names and not "Global Registration custom pre" and "... post"?

$ rg custom
...
app/views/unattended/provisioning_templates/finish/kickstart_default_finish.erb
35:<%= snippet_if_exists(template_name + " custom pre") -%>
83:<%= snippet_if_exists(template_name + " custom post") -%>
...
same for Preseed/AutoYaSt templates

[stejskalleos]

However, why did you go with these names and not "Global Registration custom pre" and "... post"?

I liked before_registration more than Global Registration custom pre. I wanted to do it the same way as the Rails callbacks.

[ekohl]

My objection is that now they're not alphabetically sorted together. A suffix will naturally group them together when you browse.