move telemetry-related settings to the config file

[kirbyquerby]

context: #3816 (comment)

The metrics-level and metrics-backend configuration for internal metrics are currently configured using command-line flags. Since config is already loaded by the time telemetry collection is set up, we should be able to instead read these values from config instead, eg:

...
service:
  telemetry:
    metrics-level: basic
    metrics-backend: opencensus
  pipelines:  
...

/cc @tigrannajaryan @bogdandrutu @odeke-em

[alolita]

@Aneurysm9 @codeboten can you please review the PR by @kirbyquerby ty!

[tigrannajaryan]

We will also likely want to specify in this same section the Resource attributes that the Collector will use in its own telemetry, particularly:

• service.namespace
• service.name (default to e.g. "io.opentelemetry.collector")
• service.instance.id (default to autogenerated as currently)
• other user-specified attributes.

For example:

service:
  telemetry:
    resource:
      service.namespace: onlineshop
      deployment.environment: production

[bogdandrutu]

The initial request from this issue is done.