Add possibility to disable metrics coming from OTC

[mat-rumian]

###### Description

New variable otelcol.metrics_enabled gives possibility to disable or enable (false/true) metrics coming from OpenTelemetry Collector. Changes are touching otc-service configuration (ports), otc-deployment (additional argument in command), values.yaml (default value).

Expected log when metrics are enabled:
{"level":"info","ts":1602188423.6246598,"caller":"service/service.go:256","msg":"Setting up own telemetry..."} {"level":"info","ts":1602188423.6251273,"caller":"service/telemetry.go:100","msg":"Serving Prometheus metrics","address":":8888","legacy_metrics":false,"new_metrics":true,"level":3,"service.instance.id":"c8020a8f-9ccb-4d98-8619-b0ddf1f24331"} {"level":"info","ts":1602188423.6261094,"caller":"service/service.go:293","msg":"Loading configuration..."}

Expected log when metrics are disabled:
{"level":"info","ts":1602188357.0610797,"caller":"service/service.go:256","msg":"Setting up own telemetry..."} {"level":"info","ts":1602188357.0619454,"caller":"service/service.go:293","msg":"Loading configuration..."} {"level":"info","ts":1602188357.0664148,"caller":"service/service.go:304","msg":"Applying configuration..."}

###### Testing performed

Tested on test cluster.

[sumo-drosiek]

I would rather put it as otelcol.metrics_enabled than sumologic.traces.otc_metrics.enabled, because its about otelcol not sumologic per se

[pmm-sumo]

+1 on Dominik's suggestion. Also, we need to update the list of params with this attribute. Otherwise, it's a nice and clean PR 👍

[pmm-sumo]

Looks good. I am only wondering if we should enable or disable it by default... hmm. @sumo-drosiek and @perk - what's your take?

[sumo-drosiek]

What are the other metrics levels?

[mat-rumian]

I didn't find anything about levels description but levels itself are described here Looks like to get information what's under which level you have to go thru the code.

[sumo-drosiek]

@pmaciolek, @mat-rumian How big is expected metrics load from the opentelemetry collector?

[pmm-sumo]

@pmaciolek, @mat-rumian How big is expected metrics load from the opentelemetry collector?

Not sure on DPM, but depending on the setup I think that there are typically ~50 metrics (including histograms)

[perk-sumo]

There is a follow-up PR: #1037