Improve documentation of resource_attributes_as_tags (#29765)

**Description:** <Describe what has changed.>
This PR improves documentation of `resource_attributes_as_tags`.

**Link to tracking Issue:** 
Closes #29702

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

exporter/datadogexporter/examples/collector.yaml

@@ -227,9 +227,11 @@ exporters:
  # endpoint: https://api.datadoghq.com
 
  ## @param resource_attributes_as_tags - string - optional - default: false
- ## Set to true to add all resource attributes of a metric to its metric tags.
- ## When set to false, only a small predefined subset of resource attributes is converted
- ## to metric tags.
+ ## Set to true to add resource attributes of a metric to its metric tags.
+ ## Please note that any of the subset of resource attributes in this
+ ## list https://docs.datadoghq.com/opentelemetry/guide/semantic_mapping/ are 
+ ## converted to datadog conventions and set to to metric tags whether this option
+ ## is enabled or not.
  #
  # resource_attributes_as_tags: false