Make list unique before saving it

Hello,

I removed duplicate email domains before saving the configuration form. I fixed it in MR. Please review.

Thank you!

Thank you @Binoli Lalani that looks quite well already.

I'm unsure, if it wouldn't perhaps make sense to use this change to no more store the patterns as string with linebreaks like in the form, but instead as array of strings and re-transform for the array...

That would clean things up a bit, I guess. But a maintainer should decide.
I'm talking about this area: https://git.drupalcode.org/issue/domain_registration-3352421/-/blob/8.x-...

If you'd like to implement that change (incl. an update hook) I'ld suggest doing it in a separate MR so the maintainer can decide.

Let's for now leave this "Needs review".

I'm not sure we want to change this here, the only thing this MR should do is to clean duplicated patterns (as I understand the issue), right?

Setting to NW.

Re #6 yes of course we can solve #5 in a follow-up!
But would make sense to solve, wouldn't it?

I think preprocess on save and store the sanitized value makes a lot of sense :)