fix: Prevent users from setting an already used username

[flacial]

Description

This PR aims to prevent users from setting an already used username when trying to change their username to avoid introducing bugs in the system.

Currently, there is no way to prevent users from setting their username to one that is already in use by another user. This can lead to bugs in the system because the system expects unique usernames. For example, when a user changes their username to an already used one and then goes to their profile page, the userInfo data returned may be for a different user.

This PR adds a check to ensure that a user cannot set their username to an already used one.

Changes Made

• Added a check to ensure that a user cannot set their username to an already used one.

Testing instructions

0. Login in
1. Navigate to the settings/account page.
2. Attempt to change your username to one that is already in use by another user.
3. Observe that the username change is not allowed, and an error message is displayed.

Related issues

• Closes Prevent users from setting an already used username #2650

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[codecov]

Codecov Report

Merging #2651 (b69e615) into master (9065dce) will not change coverage.
The diff coverage is 100.00%.

❗ Current head b69e615 differs from pull request most recent head 295ef64. Consider uploading reports for the commit 295ef64 to get more accurate results

@@            Coverage Diff            @@
##            master     #2651   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          189       189           
  Lines         3473      3476    +3     
  Branches       960       961    +1     
=========================================
+ Hits          3473      3476    +3     

Impacted Files	Coverage Δ
pages/settings/account/index.tsx	100.00% <ø> (ø)
graphql/resolvers/userDataCrud.ts	100.00% <100.00%> (ø)

[vercel]

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Name	Status	Preview	Updated
c0d3-app	✅ Ready (Inspect)	Visit Preview	Dec 27, 2022 at 11:47AM (UTC)