[chore][exporter/datadog] Improve documentation for hostname and host_metadata::hostname_source settings (open-telemetry#31702)

**Description:**

Improves documentation on the `hostname` and
`host_metadata::hostname_source` settings based on feedback from open-telemetry#29866

**Link to tracking Issue:** Fixes open-telemetry#29866

Author: mx-psi

exporter/datadogexporter/config.go

@@ -319,8 +319,12 @@ type LogsConfig struct {
 // TagsConfig defines the tag-related configuration
 // It is embedded in the configuration
 type TagsConfig struct {
-	// Hostname is the host name for unified service tagging.
-	// If unset, it is determined automatically.
+	// Hostname is the fallback hostname used for payloads without hostname-identifying attributes.
+	// This option will NOT change the hostname applied to your metrics, traces and logs if they already have hostname-identifying attributes.
+	// If unset, the hostname will be determined automatically. See https://docs.datadoghq.com/opentelemetry/schema_semantics/hostname/?tab=datadogexporter#fallback-hostname-logic for details.
+	//
+	// Prefer using the `datadog.host.name` resource attribute over using this setting.
+	// See https://docs.datadoghq.com/opentelemetry/schema_semantics/hostname/?tab=datadogexporter#general-hostname-semantic-conventions for details.
 	Hostname string `mapstructure:"hostname"`
 }
 
@@ -365,11 +369,15 @@ type HostMetadataConfig struct {
 	Enabled bool `mapstructure:"enabled"`
 
 	// HostnameSource is the source for the hostname of host metadata.
+	// This hostname is used for identifying the infrastructure list, host map and host tag information related to the host where the Datadog exporter is running.
+	// Changing this setting will not change the host used to tag your metrics, traces and logs in any way.
+	// For remote hosts, see https://docs.datadoghq.com/opentelemetry/schema_semantics/host_metadata/.
+	//
 	// Valid values are 'first_resource' and 'config_or_system':
 	// - 'first_resource' picks the host metadata hostname from the resource
 	//    attributes on the first OTLP payload that gets to the exporter.
 	//    If the first payload lacks hostname-like attributes, it will fallback to 'config_or_system'.
-	//    Do not use this hostname source if receiving data from multiple hosts.
+	//    **Do not use this hostname source if receiving data from multiple hosts**.
 	// - 'config_or_system' picks the host metadata hostname from the 'hostname' setting,
 	//    If this is empty it will use available system APIs and cloud provider endpoints.
 	//

exporter/datadogexporter/examples/collector.yaml

@@ -171,8 +171,12 @@ exporters:
   # The Datadog exporter is necessary for exporting telemetry signals to Datadog.
   datadog:
     ## @param hostname - string - optional
-    ## A custom hostname.
-    ## If unset, this will be determined automatically if possible.
+    ## The fallback hostname used for payloads without hostname-identifying attributes.
+    ## This option will NOT change the hostname applied to your metrics, traces and logs if they already have hostname-identifying attributes.
+    ## If unset, the hostname will be determined automatically. See https://docs.datadoghq.com/opentelemetry/schema_semantics/hostname/?tab=datadogexporter#fallback-hostname-logic for details.
+    ## 
+    ## Prefer using the `datadog.host.name` resource attribute over using this setting.
+    ## See https://docs.datadoghq.com/opentelemetry/schema_semantics/hostname/?tab=datadogexporter#general-hostname-semantic-conventions for details.
     #
     # hostname: customhostname
 
@@ -373,8 +377,9 @@ exporters:
     ## Host metadata specific configuration.
     ## Host metadata is the information used for populating the infrastructure list, the host map and providing host tags functionality within the Datadog app.
     ##
-    ## The exporter will only send host metadata for a single host, whose name is chosen
+    ## By default, the exporter will only send host metadata for a single host, whose name is chosen
     ## according to `host_metadata::hostname_source`.
+    ## See https://docs.datadoghq.com/opentelemetry/schema_semantics/host_metadata/ to send host metadata about more hosts.
     #
     # host_metadata:
       ## @param enabled - boolean - optional - default: true
@@ -384,10 +389,14 @@ exporters:
 
       ## @param hostname_source - enum - optional - default: config_or_system
       ## Source for the hostname of host metadata.
+      ## This hostname is used for identifying the infrastructure list, host map and host tag information related to the host where the Datadog exporter is running.
+      ## Changing this setting will not change the host used to tag your metrics, traces and logs in any way.
+      ## For remote hosts, see https://docs.datadoghq.com/opentelemetry/schema_semantics/host_metadata/.
+      ##
       ## Valid values are 'first_resource' and 'config_or_system':
       ## - 'first_resource' picks the host metadata hostname from the resource attributes on the first OTLP payload that gets to the exporter.
       ##    If the first payload lacks hostname-like attributes, it will fallback to 'config_or_system' behavior.
-      ##    Do not use this hostname source if receiving data from multiple hosts.
+      ##    **Do not use this hostname source if receiving data from multiple hosts**.
       ##
       ## - 'config_or_system' picks the host metadata hostname from the 'hostname' setting, falling back to system and cloud provider APIs.
       ##