Resolve Emoji Support in User Display Names

[gkatrakazas]

Following a comment from @emlun in PR wwWallet/wallet-frontend#170, we've identified a crash related to emoji characters in displayName. The error ER_TRUNCATED_WRONG_VALUE_FOR_FIELD occurs when emojis are used, as shown in the comment wwWallet/wallet-frontend#170 (comment):

"QueryFailedError: Incorrect string value: '\xF0\x9F...' for column wallet.user.displayName... This also fails with a single "😂", but succeeded after I removed all of the "😂"s."

Options:

• Update Backend Database Schema: Change the displayName field's character set to utf8mb4 to support emojis.
• Frontend Validation: Prevent emoji input in the displayName field on the frontend.

Action Needed: Decide between updating the backend to support emojis or restricting their use on the frontend.