fix: adding value length check for full name field

[DmytroAlipov]

Description

Fixing an error when a new user tries registering on the platform with a full name longer than 255 characters.

Now the request to the backend will not be sent because validation fails:

I also created a MR#34577 to Platform so that the backend would not miss such errors. But validation on the backend is just a fuse. It’s better not to send an invalid request to the backend.

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[mphilbrick211]

Hi @openedx/2u-vanguards! This is all set for review.