Add option --strip-confidential to the --list-packets command.

[ni4]

Description

This option may be useful when debugging certain key/signature issues, when userid/keyid/other confidential information should not be revealed.

[antonsviridenko]

What exactly this option should do? Drop everything confidential (like secret key material) from the output or hide/replace by placeholder characters? Almost everything can be considered confidential.

[ni4]

@antonsviridenko aside of secret key material it should also strip userids, keyids/fingerprintg (maybe leaving 1-2 chars to be able to distinguish between keys/subkeys). I.e. instead of userid [email protected] print p****@m***** (number of * should be fixed). Instead of keyid/fingerprint print 0x*********1F (number of * should be the same as in the original keyid/fingerprint.). Maybe some other things should be replaced as well.