add protobuf parser

[ssoroka]

Feature Request

Add a protobuf parser that lets Telegraf users specify a path to a .proto file and the parser uses it to parse a message into a metric. Would need to specify:

• what field and format the timestamp is
• what fields are tags
• what field, if any, is the measurement name

Note this will require stream parser support, which is not fully supported yet, and will need to be done as part of this work.

Use case:

for example, Sparkplug B is MQTT with protobuf message body.