Fix password validator for short domains

[JoonasAapro]

🎩 What? Why?

Decidim's password validator had been updated, which caused some changes in the method of checking the similarity with the user's email address' domain. This caused problems with registration if the user had an email address with a short domain.
For example if the email was "example@1.lvh.me", the validator would pick the first part of the domain, which in this case is "1", and check if your password had a string that matches the domain's first part, so even a password like "RndmG3951984" would fail.
After this fix the validator checks all parts of the email domain - In this example "1", "lvh" and "me"
and compares the length of the strings to a configurable number (default "4"). If the part of the domain is shorter than the number set, the validator ignores it, in this example it wouldn't validate any part of the domain with the default value.
If the domain is for example "@decidim.com" and you try to register with a password like "eX4mpl3DeCiDim", it will tell you it's too similar with the email, the validation is not case sensitive.

The domain length check was already in use with another method which compared the password to the site's domain. The checker has now been moved to it's own method that is used in both validations - email domain and site's domain. The length variable has also been made configurable

Testing

To reproduce the bug in Decidim, go to the "Sign up" -page, fill in the user information. In email field put "1.lvh.me" for example, and try to make a password containing the number "1", this will fail.

♥️ Thank you!

[alecslupu]

Tested on local, and i could confirm the fix.

i have tried with the following credentials :
system@1.example.tld => password1password1 (initially i got the error )

After Applying the patch,

system@1.example.tld => password1password1 (worked )
test@1.example.tld => password1tespassword1tes (worked)
test@1.example.tld => password1testpassword1test (successfully seen the error message "to similar....")

[alecslupu]

@JoonasAapro I have changed this PR to a change since you are adding a new parameter.
The functionality works as expected, but, in order to merge this PR, we would need a few words about this change in the RELEASE_NOTES.md file

I would say that this section from RELEASE_NOTES.md is a good example on how structure your data.

[andreslucena]

Hi @JoonasAapro, welcome to Decidim!
Great PR and fix 👏🏽 👏🏽
I found a couple of changes to be made and that'd be good to go for me.

I am dismissing Andres's review in order to merge, as the changes requested have been implemented.