FEATURE: add new --skip-email-setup parameter to discourse-setup

[ZogStriP]

Using:

./discourse-setup --skip-email-setup

We can now set up a new instance without having to set up email. It all gets skipped, and core switches to using Discourse ID as the login method. And with Discourse ID enabled, users can create accounts without the instance having the ability to send emails.

See also discourse/discourse#36731

[pmusaraj]

@ZogStriP I ran this twice on a new container, and it failed on this step:

https://github.com/discourse/discourse_docker/blob/master/templates/web.template.yml#L27

Which makes sense. To continue testing, I removed that line from the template, and then the setup continued until:

I, [2025-10-20T18:45:20.881465 #1]  INFO -- :
I, [2025-10-20T18:45:20.890094 #1]  INFO -- : File > /usr/local/bin/configure-letsencrypt  chmod: +x  chown:
I, [2025-10-20T18:45:20.897843 #1]  INFO -- : File > /usr/local/bin/letsencrypt  chmod: +x  chown:
I, [2025-10-20T18:45:20.899064 #1]  INFO -- : > echo "Beginning of custom commands"
I, [2025-10-20T18:45:20.902298 #1]  INFO -- : Beginning of custom commands

I, [2025-10-20T18:45:20.903118 #1]  INFO -- : > rails r "SiteSetting.enable_discourse_id = true"
bundler: failed to load command: script/rails (script/rails)
/var/www/discourse/lib/site_settings/type_supervisor.rb:271:in `validate_value': enable_discourse_id: You must configure Discourse ID credentials ('discourse_id_client_id' and 'discourse_id_client_secret') before enabling this setting. (Discourse::InvalidParameters)

[ZogStriP]

@pmusaraj LGTM 👍

(I can't self-approved)