It's safer for dovecot to export metrics via a UDS instead of tcp port,
this will add support for that option.
### Required for all PRs:
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- [x] Updated associated README.md.
- [x] Wrote appropriate unit tests.
resolves#9215
dovecot: Add support for unix domain sockets as well
Paweł Żak
Joshua Powers
Josef Johansson
Helen Weller
Michele Fadda