Bug report: PGP Sign operation creates encrypted output, while it should be signed cleartext.

The PGP Sign function currently uses the box function from kbpgp. The box-function is meant for encryption. While it is functional it is not creating the correct output. The clearsign function from kbpgp should be used instead. This will create an RFC4880-compliant message with human-readable text and a PGP signature.

**To Reproduce**
Select the PGP Sign funtion.
Supply a private key and passphrase
Add some random input

The result is a PHP message with the header:
"-----BEGIN PGP MESSAGE-----"

Using the clearsign will create a message with the header:
"-----BEGIN PGP SIGNED MESSAGE-----"

**Additional context**
I have created PR #2696 to change the function from kbpgp.box to kbpgp.clearsign,

Start at the CyberChef PGP Sign operation and inspect its use of kbpgp.box. Compare the reproduced output header with the expected cleartext-signed format, then review PR #2696 and verify the operation with a private key, passphrase, and sample input; done means it produces the RFC4880-style signed-message header rather than an encrypted-message header.

Written by the indexing model from the issue text.