Provide documentation for Solace PubSub+ Event Broker scaler (kedacor…

…e#486)

Signed-off-by: Dennis Brinley <dennis.brinley@solace.com>

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content/docs/2.4/scalers/solace.md

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+title = "Solace PubSub+ Event Broker"
+availability = "2.4+"
+maintainer = "Community"
+description = "Scale applications based on Solace PubSub+ Event Broker Queues"
+layout = "scaler"
+go_file = "solace_scaler"
++++
+
+### Trigger Specification
+This specification describes the `solace-event-queue` trigger that scales based on a Solace PubSub+ Event Broker queue.
+
+```yaml
+triggers:
+- type: solace-event-queue
+  metadata:
+    solaceSempBaseURL:        http://solace_broker:8080
+    messageVpn:               message-vpn
+    queueName:                queue_name
+    messageCountTarget:       '100'
+    messageSpoolUsageTarget:  '100'       ### Megabytes (MB)
+    username:                 semp-user
+    password:                 semp-pwd
+    usernameFromEnv:          ENV_VAR_USER
+    passwordFromEnv:          ENV_VAR_PWD
+```
+
+**Parameter list:**
+- `solaceSempBaseURL` - Solace SEMP Endpoint in format: `<protocol>://<host-or-service>:<port>`
+- `messageVpn` - Message VPN hosted on the Solace broker.
+- `queueName` - Message Queue to be monitored
+- `messageCountTarget` - The target number of messages manageable by a pod. The scaler will cause the replicas to increase if the queue message backlog is greater than the target value per active replica.
+- `messageSpoolUsageTarget` - Integer value expressed in Megabytes (MB). The target spool usage manageable by a pod. The scaler will cause the replicas to increase if the queue spool usage is greater than the target value per active replica.
+- `username` - User account with access to Solace SEMP RESTful endpoint
+- `password` - Password for the user account
+- `usernameFromEnv` - Environment variable set with SEMP user account
+- `passwordFromEnv` - Environment variable set with password for the user account
+
+**Parameter Requirements:**
+- Parameters resolving the target queue are all **required:** `solaceSempBaseURL`, `messageVpn`, `queueName`
+- **At least** one of `messageCountTarget` or `messageSpoolUsageTarget` is **required.** If both values are present, the metric value resulting in the higher desired replicas will be used. (Standard KEDA/HPA behavior)
+- The Solace PubSub+ Scaler polls the Solace SEMP REST API to monitor target queues. Currently, the scaler supports basic authentication. `username` and `password` are **required** for the `solace-event-queue` trigger to function. These values may be set directly in the trigger metadata or using a TriggerAuthentication record. See [Authentication Parameters](#authentication-parameters) below. Alternatively, credentials may be passed from environment variables identified by `usernameFromEnv` and `passwordFromEnv`.
+
+### Authentication Parameters
+You can use TriggerAuthentication CRD to configure the username and password to connect to the management endpoint.
+
+**Username and Password based authentication:**
+- `username` Required. The username to use to connect to the Solace PubSub+ Event Broker's SEMP endpoint.
+- `password` Required. The password to use to connect to the Solace PubSub+ Event Broker's SEMP endpoint.
+
+### Example
+The objects in the example below are declared in `namespace=solace`. It is not required to do so. If you do define a namespace for the configuration objects, then they should all be delcared in the same namespace.
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name:      solace-secret
+  namespace: solace
+  labels:
+    app: solace-consumer
+type: Opaque
+data:
+  SEMP_USER:         YWRtaW4=
+  SEMP_PASSWORD:     S2VkYUxhYkFkbWluUHdkMQ==
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name:      solace-scaled-object
+  namespace: solace
+spec:
+  scaleTargetRef:
+    apiVersion:    apps/v1
+    kind:          Deployment
+    name:          solace-consumer
+  pollingInterval: 20
+  cooldownPeriod:  60
+  minReplicaCount:  0
+  maxReplicaCount: 10
+  triggers:
+  - type: solace-event-queue
+    metadata:
+      solaceSempBaseURL:       http://broker-pubsubplus.solace.svc.cluster.local:8080
+      messageVpn:              test_vpn
+      queueName:               SCALED_CONSUMER_QUEUE1
+      messageCountTarget:      '50'
+      messageSpoolUsageTarget: '100000'
+    authenticationRef: 
+      name: solace-trigger-auth
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: solace-trigger-auth
+  namespace: solace
+spec:
+  secretTargetRef:
+    - parameter:   username
+      name:        solace-secret
+      key:         SEMP_USER
+    - parameter:   password
+      name:        solace-secret
+      key:         SEMP_PASSWORD
+```