add orchestrator explorer support in pkg/datadog/config (open-telemetry#44105)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

This change introduces a new orchestrator_explorer configuration in
pkg/datadog/config, which is disabled by default.
The configuration will be used to collect Kubernetes resource data and
send it to Datadog. This functionality is currently a work in progress.

The overall goal is to keep it aligned with the configuration used in
the Datadog agent:
https://github.com/DataDog/helm-charts/blob/main/charts/datadog/values.yaml#L887-L892

<!--Describe what testing was performed and which tests were added.-->
#### Testing
It is covered by unit test `TestValidate`

Co-authored-by: Pablo Baeyens <[email protected]>

Author: kangyili

.chloggen/datadog-config_orchestrator-explorer.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/filelog)
+component: pkg/datadog
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: add orchestrator explorer support in pkg/datadog/config
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [44105]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

pkg/datadog/config/config.go

@@ -110,6 +110,8 @@ type Config struct {
 	// `use_resource_metadata`, or `host_metadata::hostname_source != first_resource`
 	OnlyMetadata bool `mapstructure:"only_metadata"`
 
+	OrchestratorExplorer OrchestratorExplorerConfig `mapstructure:"orchestrator_explorer"`
+
 	// Non-fatal warnings found during configuration loading.
 	warnings []error
 }
@@ -175,6 +177,10 @@ func (c *Config) Validate() error {
 		return errors.New("reporter_period must be 5 minutes or higher")
 	}
 
+	if err := c.OrchestratorExplorer.Validate(); err != nil {
+		return err
+	}
+
 	return nil
 }
 
@@ -403,6 +409,10 @@ func CreateDefaultConfig() component.Config {
 			ReporterPeriod: 30 * time.Minute,
 		},
 
+		OrchestratorExplorer: OrchestratorExplorerConfig{
+			Enabled: false,
+		},
+
 		HostnameDetectionTimeout: 25 * time.Second, // set to 25 to prevent 30-second pod restart on K8s as reported in issue #40372 and #40373
 	}
 }

pkg/datadog/config/config_test.go

@@ -201,6 +201,18 @@ func TestValidate(t *testing.T) {
 			},
 			err: "reporter_period must be 5 minutes or higher",
 		},
+		{
+			name: "empty cluster_name when orchestrator_explorer is enabled",
+			cfg: &Config{
+				API:          APIConfig{Key: "abcdef0"},
+				HostMetadata: HostMetadataConfig{Enabled: true, ReporterPeriod: 10 * time.Minute},
+				OrchestratorExplorer: OrchestratorExplorerConfig{
+					Enabled:     true,
+					ClusterName: "",
+				},
+			},
+			err: "'cluster_name' is required when 'orchestrator_explorer' is enabled",
+		},
 	}
 	for _, testInstance := range tests {
 		t.Run(testInstance.name, func(t *testing.T) {

pkg/datadog/config/orchestrator_explorer.go

@@ -0,0 +1,23 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package config // import "github.com/open-telemetry/opentelemetry-collector-contrib/pkg/datadog/config"
+
+import "errors"
+
+// OrchestratorExplorerConfig defines configuration for the Datadog orchestrator explorer.
+type OrchestratorExplorerConfig struct {
+	// Enabled enables the orchestrator explorer.
+	Enabled bool `mapstructure:"enabled"`
+
+	// ClusterName defines the kubernetes cluster name.
+	ClusterName string `mapstructure:"cluster_name"`
+}
+
+// Validate the configuration for errors.
+func (c *OrchestratorExplorerConfig) Validate() error {
+	if c.Enabled && c.ClusterName == "" {
+		return errors.New("'cluster_name' is required when 'orchestrator_explorer' is enabled")
+	}
+	return nil
+}