feat: Templated names and tags for Consul targets

[nlgotz]

This adds the ability to use Go Templates on Consul targets to set both the name of the target as well as event-tags. The primary driving force for this comes from Telegraf's Prometheus Input Plugin which also has Consul support and allows for using Go templates to set the name/tags as well.

As an example, you are now able to do something like:

loader:
    type: consul
    address: consul:8500
    datacenter: "dc99"
    services:
        - name: gnmic-sros
          target-name: "{{.Meta.device}}"
          target-tags:
              region: "{{.Meta.region}}"
              geo: "{{.Meta.geo}}"
              test: "{{.Meta.test}}"

This also removes a debugging statement in pkg/config/loader.go that could potentially expose passwords in log messages

[karimra]

Why not use the existing fields under config? They can be set to some Go template, the only missing piece is to execute them.
To use your example, it would look like:

loader:
    type: consul
    address: consul:8500
    datacenter: "dc99"
    services:
        - name: gnmic-sros
          config:
            name: "{{.Meta.device}}"
            event-tags:
              region: "{{.Meta.region}}"
              geo: "{{.Meta.geo}}"
              test: "{{.Meta.test}}"

[nlgotz]

@karimra - updated to use the config section to work with that example config. It's is much cleaner

[karimra]

Thanks for the contribution! And sorry for the delay.