Fix escaping for Telegraf StatsD

[shakuzen]

I tried to look into this but cannot find specific documentation on it. Here it says (emphasis added):

Since InfluxDB supports tags, our StatsD implementation does too! Adding tags to a StatsD metric is similar to how they appear in line-protocol.

It says similar but that leaves the possibility it isn't exactly the same. Going to the documentation on Influx's line-protocol there is this section, which describes needing to escape commas, spaces, and equals signs depending on the place.

Originally posted by @shakuzen in #6450 (comment)