Capitalized letters in username silently gets converted to lowercase

Describe the bug

While writing tests with Cypress, I found that in the /settings page when you try to change your username with a capital letter, it silently get’s converted to lowercase. For example: if Quincy was input, it get’s converted to quincy.

To Reproduce Steps to reproduce the behavior:

1. Go to ‘/setting’
2. Click on the username change input and enter a username with capital letter
3. Click Save
4. See the issue

Expected behavior

It should show an error message or warn the user that capital letters in name will get converted to lowercase.

[raisedadead]

Since we haven’t had any objections lets go with Username (lowercase only).

[ojeytonwilliams]

Sure. What I’m suggesting is that it’s forced to be lowercase by validation, so you can’t click submit until all the characters are lowercase.

To be on the safe side, I think we should validate in here

https://github.com/freeCodeCamp/freeCodeCamp/blob/a48ed627adaeed622a099b87d990d917b65a7561/api-server/common/models/user.js#L730

as well.