devel/awscli: use mandoc instead of groff, suggest auto-complete

Add patch from PR 240664 to use mandoc instead of groff, and remove the
DOCS option and runtime dependency on groff. Bump PORTREVISION due to
the change in package dependencies.

While here, add pkg-message with instructions on how to enable auto-
complete for awscli.

PR: 240664
Submitted by: nork@ninth-nine.com
Sponsored by: Miles AS