Add new branch protection rules for Docker config tests

[mpguerra]

We need 4 new branch protection rules now that #7616 has merged:

• Test CD default Docker config file / Test default-conf in Docker
• Test CD custom Docker config file / Test custom-conf in Docker
• Test CI default Docker config file / Test default-conf in Docker
• Test CI custom Docker config file / Test custom-conf in Docker

Originally posted by @teor2345 in #7616 (comment)

[mpguerra]

Can we have someone other than @gustavovalverde or @teor2345 take this one so we spread knowledge on this around the team?
There's documentation on this in #7773

[upbqdn]

I tried adding the rules, but I can't see the "Branches" section in the settings. I guess I don't have the permissions.

[gustavovalverde]

As I was reassigned to this, I've recently added these rules.