mail/stalwart-cli: New port: Stalwart Mail Server CLI

stalwart-cli is the command line interface tool for managing a
Stalwart Mail Server installation. It interacts with the server's
JMAP-based administration API.

WWW: https://stalw.art/

PR: 295647
Reported by: Adrian Gschwend <ktk@netlabs.org> (initial patch),

		Herbert J. Skuhra <herbert@gojira.at> (committed patch)

Reviewed by: Orville Q. Song <orville@anislet.dev>
Approved by: Orville Q. Song <orville@anislet.dev> (new maintainer)
Co-authored-by: Adrian Gschwend <ktk@netlabs.org>