Mailqueue-runner

- All CLI tools like `mq-mail` and `mq-sendmail` now ensure that sent messages use `CRLF` (`\r\n`) as mandated by the SMTP RFCs (a045882c868be93ddf160aeeb11f02b45da49657). Some SMTP servers reject messages which use only `LF` (`\n`).
- `mq-send-test`: provide feedback for interactive terminals (aa8207f1d24123a36d8543b52325cd5e96725b32)
- `mq-send-test`: prefer `from` setting from config file if `--from=...` is not set (ac615d5af342800c79b15b1a665b8bd61f10a092)
- also run tests for Python 3.13

- `mq-sendmail` now accepts default CLI parameters from cronie (9438e4144a0a879fe17a9cdca0531291f3911188). This means cronie can send emails containing the output of cron jobs if `mq-sendmail` is available under `/usr/sbin/sendmail`.
- The RPM package now uses the `alternatives` mechanism to provide implementations for `/usr/sbin/sendmail` and `/usr/bin/mail` so that cronie and dnf-automatic can send their emails via mailqueue-runner.

- `mq-mail`: provide (very limited) replacement for `/usr/bin/mail`
- `mq-sendmail` now also supports `-t`/`--read-recipients`
- avoid warnings when executing `mq-run` when the queue folder was missing some maildir subdirectories (5ccb66da8255e303a6eb0981e10af777db23f6bd)
- Simplify logging of email deliveries when using the CLI tools `mq-run`, `mq-mail`, ... (ae12b28cec28a34e2d4477fc406e2325b1d1bf03)

- `mq-sendmail`: a bare-bones CLI script which can replace `/usr/bin/sendmail`
- CLI scripts now load config from well-known locations by default (`~/.mailqueue-runner.conf`, `/etc/mailqueue-runner.conf`)
- `PuzzlePluginSystem` is now an optional dependency
- dropped support for Python 2
- provide dnf repository for Fedora and EL9
- fix exception in message logging when email contained 8 bit characters

Code base modernization: Library should support Python 2.7 and Python 3.6-3.12.

This will be the last release supporting Python 2.7.