Remote write compliance updates

[helenosheaa]

relates to #9166

• upgraded to prometheus/common v0.15.0 as it includes an update to text parsing to not allow duplicate labels

this change will mean we pass the prometheus remote write repeated labels compliance test which we are currently failing

• added a check to the prometheus serializer to see if the tags value is "", if it is we drop the tag

this change will mean we mass the prometheus remote write empty labels compliance test, added a test for the above

[telegraf-tiger]

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• darwin_amd64.tar.gz

• windows_amd64.zip

• windows_i386.zip

• aarch64.rpm

• armel.rpm

• armv6hl.rpm

• i386.rpm

• ppc64le.rpm

• s390x.rpm

• x86_64.rpm

• freebsd_amd64.tar.gz

• freebsd_i386.tar.gz

• linux_amd64.tar.gz

• linux_arm64.tar.gz

• linux_armel.tar.gz

• linux_armhf.tar.gz

• linux_i386.tar.gz

• linux_mips.tar.gz

• linux_mipsel.tar.gz

• linux_ppc64le.tar.gz

• linux_s390x.tar.gz

• static_linux_amd64.tar.gz

• amd64.deb

• arm64.deb

• armel.deb

• armhf.deb

• i386.deb

• mips.deb

• mipsel.deb

• ppc64el.deb

• s390x.deb