Fix: Added alternative username to use when username is taken

[Nikash-B]

Currently, users don't see any other usernames to try when the username they tried is taken.

We enabled NodeBB to display an alternative username when the username input during account creation was taken. This enables users to try different usernames.

The primary code changes were modifying the username-taken string to also taken in another string, here the username input, in public/language/en-US/error.json and public/src/client/register.js to insert the username along with the suffix as a potential alternative username that the user could try while creating their account.

This PR closes #1.

We can see using the screenshot below that fix is working.

[coveralls]

Pull Request Test Coverage Report for Build 21594715295

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.841%

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Totals
Change from base Build 21503398961:	0.0%
Covered Lines:	25358
Relevant Lines:	30328

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💛 - Coveralls