cannot import public key longer than 20kb

[martgil]

Description: The user is unable to import the key because it has 20.24kb while our input fields currently have a limit of 20kb characters.

Sample public key has 20.24kb - https://flowcrypt.com/attester/pub/A62F3CDFECC0926C

Reference: https://mail.google.com/mail/u/human@flowcrypt.com/#inbox/FMfcgzGslbKpfTcJlrrsQzJnWJzgHQzn