add PredictKube Scaler docs (#617)

Signed-off-by: Daniel Yavorovych <daniel.yavorovich@gmail.com>

content/docs/2.6/scalers/predictkube.md

@@ -0,0 +1,111 @@
++++
+title = "Predictkube"
+availability = "v2.6+"
+maintainer = "Dysnix"
+description = "AI-based predictive scaling based on Prometheus metrics & PredictKube SaaS."
+layout = "scaler"
+go_file = "predictkube_scaler"
++++
+
+PredictKube is an open-source project with the SAAS part consisting of an AI model that requires API to connect to the project for the main functions of predicting and scaling.
+
+To make our AI model access your data and make a prediction based on it, please use the API key we'll send to your e-mail.
+
+Review our [Privacy Policy](https://predictkube.com/privacy-policy) to see how your data circulates in and out PredictKube.
+
+### Trigger Specification
+
+This specification describes the `predictkube` trigger that scales based on a predicting load based on `prometheus` metrics.
+
+```yaml
+triggers:
+- type: predictkube
+  metadata:
+    # Required fields:
+    predictHorizon: "2h"
+    historyTimeWindow: "7d"
+    prometheusAddress: http://<prometheus-host>:9090
+    query: sum(rate(http_requests_total{deployment="my-deployment"}[2m]))
+    queryStep: "2m"
+    threshold: '100'
+```
+
+**Parameter list:**
+
+- `predictHorizon` - Prediction time interval. It is usually equal to the cool-down period of your application.
+- `historyTimeWindow` - Time range for which to request metrics from Prometheus. We recommend using minimum 7-14 days time window as historical data.
+- `prometheusAddress` - Address of Prometheus server.
+- `query` - Predict the query that will yield the value for the scaler to compare against the `threshold`. The query must return a vector/scalar single element response.
+- `queryStep` - The maximum time between two slices within the boundaries for QML range query, used in the query.
+- `threshold` - Value to start scaling for.
+
+### Authentication Parameters
+
+Predictkube Scaler supports one type of authentication - authentication by API key.
+Prometheus used in Predictkube Scaler supports all authentication methods that are available in Prometheus Scaler.
+
+**Auth gateway based authentication:**
+
+- `apiKey` - API key previously issued for this tenant. You can get your API key by clicking on any **GET API KEY** button on the [website of PredictKube](https://predictkube.com/)
+
+### Example
+
+```yaml
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: predictkube-secrets
+  namespace: some-namespace
+type: Opaque
+data:
+  apiKey: # Required: base64 encoded value of PredictKube apiKey
+  bearerToken: "BEARER_TOKEN" # Optional: bearer authentication for Prometheus
+  ca: "CUSTOM_CA_CERT" # Optional: certificate authority file for TLS client authentication for Prometheus
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: keda-trigger-auth-predictkube-secret
+  namespace: some-namespace
+spec:
+  secretTargetRef:
+    # Required: API key for your predictkube account
+  - parameter: apiKey
+    name: predictkube-secrets
+    key: apiKey
+    # Optional: might be required if you're using bearer auth for Promethrus
+  - parameter: bearerToken
+    name: keda-prom-secret
+    key: bearerToken
+    # Optional: might be required if you're using a custom CA for Promethrus
+  - parameter: ca
+    name: keda-prom-secret
+    key: ca
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name: predictkube-scaledobject
+  namespace: some-namespace
+spec:
+  scaleTargetRef:
+    name: my-deployment
+    kind: StatefulSet
+  pollingInterval: 30
+  cooldownPeriod: 7200
+  minReplicaCount: 3
+  maxReplicaCount: 50
+  triggers:
+  - type: predictkube
+    metadata:
+      predictHorizon: "2h"
+      historyTimeWindow: "7d"
+      prometheusAddress: http://<prometheus-host>:9090
+      query: sum(rate(http_requests_total{deployment="my-deployment"}[2m])) # Note: query must return a vector/scalar single element response
+      queryStep: "2m" # Note: query step duration for range prometheus queries
+      threshold: "100"
+      authModes: "bearer" # might be required if you're using bearer auth for Promethrus
+    authenticationRef:
+      name: keda-trigger-auth-predictkube-secret
+```