fix: added valid url check in callback url redirection

[devcer]

Context

• fixes rafiki.money vulnerability -> callbackURL parameter #1136

Changes

Added an invalid URL check before the callback URL redirection

[devcer]

@raducristianpopa @Tymmmy The new URL(...).searchParams.set(...) already encode the URL, Hence encodeURIComponent is not needed in middleware. Otherwise, it is double encoding the already encoded URL, causing other URL issues. To verify this, you could open https://rafiki.money/transactions in incognito and you will see the encoded callback param in the URL.