Bring Kafkamatrics receiver into the discovery mode

[samiura]

Description: Simple attempt to enable discovery mode for kafkamatrics receiver

Link to Splunk idea: #4903

Testing: Tested for host observer, docker observer and k8s observer without any crashes.

Sample --dry-run output:

samiura@r91395f3 [03:09:07 PM] [~/test]                                                                                                                                                                                                                                                                                                           
-> % docker run --name otelcol2 -d  \                                                                                                                                                                                                                                                                                                             
    --pid host \                                                                                                                                                                                                                                                                                                                                  
  --network host \                                                                                                                                                                                                                                                                                                                                
  --volume /var/run/docker.sock:/var/run/docker.sock \                                                                                                                                                                                                                                                                                            
   -v "${PWD}":/home/ \                                                                                                                                                                                                                                                                                                                           
       -p 4318:4318 \                                                               
quay.io/splunko11ytest/otelcol_test/otelcol:latest \                                
--config /home/splunk-otel-config1.yaml \                                           
--discovery --dry-run;                                                              
samiura@r91395f3 [03:09:11 PM] [~/test]                                             
-> % docker logs -f otelcol2

-> % docker logs -f otelcol2
2024/05/29 22:09:07 settings.go:471: Set config to [/home/splunk-otel-config1.yaml]
2024/05/29 22:09:07 settings.go:532: Set memory limit to 460 MiB
2024/05/29 22:09:07 settings.go:517: Set soft memory limit set to 460 MiB
2024/05/29 22:09:07 settings.go:407: set "SPLUNK_LISTEN_INTERFACE" to "0.0.0.0"
Discovering for next 10s...
Successfully discovered "kafkametrics" using "docker_observer" endpoint "3ced9172994ad850ff1457cd5fafc940c9e17ddba49250b899abb43b144752d3:9092".
Discovery complete.
exporters:
  signalfx:
    access_token: ACCESS_TOKEN_STRING
    drop_histogram_buckets: true
    realm: us0
  signalfx/internal:
    access_token: ACCESS_TOKEN_STRING
    realm: us0
    sync_host_metadata: true
extensions:
  docker_observer: {}
receivers:
  hostmetrics:
    collection_interval: 10s
    scrapers:
      cpu: null
      disk: null
      filesystem: null
      memory: null
      network: null
  receiver_creator/discovery:
    receivers:
      kafkametrics:
        config:
          protocol_version: 2.0.0
          scrapers:
          - brokers
          - topics
          - consumers
        resource_attributes: {}
        rule: type == "container" and any([name, image, command], {# matches "(?i)kafka.*"})
          and not (command matches "splunk.discovery")
    watch_observers:
    - docker_observer
service:
  extensions:
  - docker_observer
  pipelines:
    metrics:
      exporters:
      - signalfx
      receivers:
      - hostmetrics
      - receiver_creator/discovery
    metrics/internal:
      exporters:
      - signalfx/internal
      processors: null
      receivers:
      - hostmetrics
  telemetry:
    resource:
      splunk_autodiscovery: "true"

Documentation: