Attach and Import Public Keys Options

[TheCuteFoxxy]

Is your feature request related to a problem? Please describe.
Currently, in order to verify a signed email, you have to have the sending person physically provide you the public key and then MANUALLY import it into your keyring. Unlike other mail software that has built in options for this.

Describe the solution you'd like
Snappymail should have an option attach the public key (it attaches the signature file already) and an option import it to the user's keyring.

Describe alternatives you've considered
None, even if we get a public key from a different mail client it still has to be imported manually.

Additional context
If snappymail is being used for anyone who receives signed or encrypted mail, this adds additional steps to using the mail. As an example, I've attached a screenshot for how ProtonMail handles attaching and importing Public Keys.

[TheCuteFoxxy]

Update: Snappymail does support importing keys attached to mail, its just not obvious. If the file is attached in an appropriate format (i.e PEM) then it prompts for an import.

The key still has to be manually attached when sending however.