added docs for azure blob

content/scalers/azure-storage-blob.md

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+fragment = "content"
+weight = 100
+title = "Azure Blob Storage"
+background = "light"
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+
+Scale applications based on Azure Blob Storage.
+
+**Availability:** v1.1+ | **Maintainer:** Community
+
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `azure-blob` trigger for Azure Blob Storage.
+
+```yaml
+triggers:
+  - type: azure-blob
+    metadata:
+      blobContainerName: functions-blob # Required: Name of Azure Blob Storage container
+      blobCount: '5' # Optional. Amount of blobs to scale out on. Default: 5 blobs 
+      connection: STORAGE_CONNECTIONSTRING_ENV_NAME # Optional if TriggerAuthentication defined with pod identity or connection string authentication.
+      blobPrefix:  # Optional. Prefix for the Blob. Use this to specifiy sub path for the blobs if required. Default : ""
+      blobDelimiter: # Optional. Delimiter for identifying the blob Prefix. Default: "/"
+```
+
+The `connection` value is the name of the environment variable your deployment uses to get the connection string. This is usually resolved from a `Secret V1` or a `ConfigMap V1` collections. `env` and `envFrom` are both supported.
+
+### Authentication Parameters
+
+You can authenticate by using pod identity or connection string authentication.
+
+**Connection String Authentication:**
+
+- `connection` - Connection string for Azure Storage Account
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: azure-blob-auth
+spec:
+  podIdentity:
+    provider: azure
+---
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: azure-blob-scaledobject
+  namespace: default
+  labels:
+    deploymentName: azureblob-function
+spec:
+  scaleTargetRef:
+    deploymentName: azureblob-function
+  triggers:
+  - type: azure-blob
+    metadata:
+      # Required
+      blobContainerName: functionsblob
+      # Optional
+      blobCount: "5" # default 5
+      blobPrefix: blobsubpath # Default : ""
+      blobDelimiter: "/" # Default: "/"
+    authenticationRef:
+        name: azure-blob-auth # authenticationRef would need either podIdentity or define a connection parameter
+```