Enforce the disabled non confirmation for email users

[andreslucena]

We're getting spammed, so we want to disallow unconfirmed access in Metadecidim.

Some details related to this PR:

• We're also going to make this change upstream. Until that's approved we will force it in this app. See https://github.com/decidim/decidim/pull/8233
• I've actually already made this change here 9 months ago, although it didn't work. This time I'm also adding a spec so we don't have regressions.
• Related to the previous one, I think it didn't work because we're trying to change an initializer with another initializer or something like that. I've found the correct solution at the CodeForJapan repository