fix: name length validation

[Inferato]

According to the UserProfile limitation for the name field:
name = models.CharField(blank=True, max_length=255, db_index=True)
we need to add the validation for the name length.
A better solution would be to use the separate constant which we could use for both the model field and validation criteria, but considering that the field has been unchanged since Feb 2012 - it was rejected to simplify the fix.

Related: master

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[mphilbrick211]

Hi @openedx/2u-aperture! This is ready after the master is merged.

[robrap]

@mphilbrick211: [inform] Moved to aurora from arch-bom on Contributions board.

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@Inferato 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.

[robrap]

[inform] This one also should have been Aperture. I will fix the ownership.

Thank you for the contribution!