plugins/inputs/dovecot: Add support for unix domain sockets

[isodude]

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:

• Updated associated README.md.
• Wrote appropriate unit tests.

resolves #9215

dovecot: Add support for unix domain sockets as well

[telegraf-tiger]

Looks like new artifacts were built from this PR. Get them here!

Artifact URLs

• darwin_amd64.tar.gz

• windows_amd64.zip

• windows_i386.zip

• s390x.rpm

• linux_s390x.tar.gz

• s390x.deb

• x86_64.rpm

• freebsd_amd64.tar.gz

• linux_amd64.tar.gz

• amd64.deb

• linux_mips.tar.gz

• mips.deb

• armv6hl.rpm

• linux_armhf.tar.gz

• armhf.deb

• aarch64.rpm

• linux_arm64.tar.gz

• arm64.deb

• linux_mipsel.tar.gz

• mipsel.deb

• i386.rpm

• freebsd_i386.tar.gz

• linux_i386.tar.gz

• i386.deb

• static_linux_amd64.tar.gz

• armel.rpm

• linux_armel.tar.gz

• armel.deb

• ppc64le.rpm

• linux_ppc64le.tar.gz

• ppc64el.deb

[helenosheaa]

Thanks for opening the pr, overall I think it looks good. Do you think you could add a test for this extension of functionality?

[isodude]

During testing I discovered that Server was not populated in the returned metric.
Wrote the unix socket address instead of leaving it empty.

[telegraf-tiger]

Looks like new artifacts were built from this PR. Get them here!

Artifact URLs

• windows_amd64.zip

• windows_i386.zip

• darwin_amd64.tar.gz

• i386.rpm

• freebsd_i386.tar.gz

• linux_i386.tar.gz

• i386.deb

• linux_mips.tar.gz

• mips.deb

• aarch64.rpm

• linux_arm64.tar.gz

• arm64.deb

• static_linux_amd64.tar.gz

• linux_mipsel.tar.gz

• mipsel.deb

• s390x.rpm

• linux_s390x.tar.gz

• s390x.deb

• armv6hl.rpm

• linux_armhf.tar.gz

• armhf.deb

• armel.rpm

• linux_armel.tar.gz

• armel.deb

• x86_64.rpm

• freebsd_amd64.tar.gz

• linux_amd64.tar.gz

• amd64.deb

• ppc64le.rpm

• linux_ppc64le.tar.gz

• ppc64el.deb