Add documentation for Datadog scaler

content/docs/2.6/scalers/datadog.md

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+title = "Datadog"
+layout = "scaler"
+availability = "v2.6+"
+maintainer = "Datadog"
+description = "Scale applications based on Datadog."
+go_file = "datadog_scaler"
++++
+
+### Trigger Specification
+
+This specification describes the `datadog` trigger that scales based on a Datadog metric.
+
+```yaml
+triggers:
+- type: datadog
+  metadata:
+    query: "sum:trace.redis.command.hits{env:none,service:redis}.as_count()"
+    queryValue: "7"
+    type: "global"
+    age: "60"
+```
+
+**Parameter list:**
+
+- `query` - The Datadog query to run.
+- `queryValue` - Value to reach to start scaling.
+- `type` - Whether to start scaling based on the value or the average between pods. (Values: `average`, `global`, Default:`average`, Optional)
+- `age`: The time window (in seconds) to retrieve metrics from Datadog. (Default: `90`, Optional) 
+
+### Authentication
+
+Datadog requires both an API key and an APP key to retrieve metrics from your account.
+
+You should use `TriggerAuthentication` CRD to configure the authentication:
+
+**Parameter list:**
+- `apiKey` - Datadog API key.
+- `appKey` - Datadog APP key.
+- `datadogSite` - Datadog site where to get the metrics from. This is commonly referred as DD_SITE in Datadog documentation. (Default: `datadoghq.com`, Optional)
+
+### Example
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: datadog-secrets
+  namespace: my-project
+type: Opaque
+data:
+  apiKey: # Required: base64 encoded value of Datadog apiKey
+  appKey: # Required: base64 encoded value of Datadog appKey
+  datadogSite: # Optional: base64 encoded value of Datadog site
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: keda-trigger-auth-datadog-secret
+  namespace: my-project
+spec:
+  secretTargetRef:
+    # Required: API key for your Datadog account
+  - parameter: apiKey
+    name: datadog-secrets
+    key: apiKey
+    # Required: APP key for your Datadog account
+  - parameter: appKey
+    name: datadog-secrets
+    key: appKey
+    # Optional: Datadog site. Default: "datadoghq.com"
+  - parameter: datadogSite
+    name: datadog-secrets
+    key: datadogSite
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name: datadog-scaledobject
+  namespace: my-project
+spec:
+  scaleTargetRef:
+    name: worker
+  triggers:
+  - type: datadog
+    metadata:
+      # Required: datadog metric query
+      query: "sum:trace.redis.command.hits{env:none,service:redis}.as_count()"
+      # Required: according to the number of query result, to scale the TargetRef
+      queryValue: "7"
+      # Optional: (Global or Average). Whether the target value is global or average per pod. Default: Average
+      type: "Global"
+      # Optional: The time window (in seconds) to retrieve metrics from Datadog. Default: 90
+      age: "60"
+    authenticationRef:
+      name: keda-trigger-auth-datadog-secret
+```