fixes-#3235:userName_dup_check added some delay to call API

[PratyushSawan]

Fixes #3235

Changes:

This Fix ensures that the asyncValidate function only runs after 500ms of inactivity. It decreased the API Call significantly.
All the previous functionality working as it is.

Here is the Test Video:

fixes-.3235_userName_dup_check.-.Made.with.Clipchamp.mp4

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[lindapaiste]

It looks like you are on the right track with this approach. I suspect that we want separate timeoutId variables for the username and email checks (ie. usernameTimeoutId and emailTimeoutId). Otherwise editing one field will cancel the timeout on the other.