Disable Save button and show hint if email or default vote weight in <new account>/<new participant> is faulty

[Elblinator]

Current behaviour:
new account:
If the mask is opened and a wrong e-mail address or vote weight is put into the field the save button is not disabled and if the new account is saved the error Cannot read properties of undefined (reading '0') is displayed but the mask with every input stays on screen
new participant:
If in step 1 or step 3 in the mask a wrong email-address is assigned to the new participant then the save button is not disabled and if pressed the error Error: email must be valid email. it thrown and the are navigated back to the participant-list (the input for the new participant is being lost)

Correct input (as far as I understand it):
Correct vote weight: number >= 0.000001

Correct Email: @.
Description in words:
A correct mail-address consists out of three strings with to separators:

• a string
• "@"
• a string
• "."
• a string

Wanted behaviour:
If there is a wrong input in these masks then two things should happen:

1. the save button should be disabled
2. the input-field which has the faulty input should get coloured in the warn colour and a text should be displayed unter the line:
   • for a wrong email: "Please enter a valid email address. "
   • for a wrong vote weight: "Please select a vote weight bigger than or equal to zero."

[reiterl]

We should use a email validation from Angular or a lib. Email validation is more complex than what @Elblinator wrote.

[rrenkert]

Yes, email validation is more complex but a regex should be enough for the validation we need at this place.

[reiterl]

We should use the default Angular Validator here.

[jsangmeister]

Vote weight must be at least 0.000001, see OpenSlides/openslides-backend#1926. Updated the description.

[reiterl]

Yes, that is right, but this requirement is part of an own client issue.

[reiterl]

I have added the default vote weight Validator and error check and have updated the error message.
(To prevent zero)