Add password prompt for P12 files

[wagoodman]

Adds prompting for password input when no password was given for an encrypted P12 file:

$ quill p12 attach-chain /some/path/to/file.p12

[0000]  INFO quill version: [not provided]
[0000]  INFO attaching certificate chain to p12 file file=/some/path/to/file.p12
 ❖ Enter P12 password: ●●●●●●●●●●●●●●●