Add documentation for operator Prometheus metrics. (kedacore#945)

content/docs/2.5/operate/prometheus.md

@@ -6,6 +6,14 @@ weight = 200
 
 ## Prometheus Exporter Metrics
 
+### Operator 
+
+The KEDA Operator exposes Prometheus metrics which can be scraped on port `8080` at `/metrics`. The following metrics are being gathered:
+
+- Metrics exposed by the `Operator SDK` framework as explained [here](https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#metrics).
+
+### Metrics Adapter
+
 The KEDA Metrics Adapter exposes Prometheus metrics which can be scraped on port `9022` (this can be changed by setting the `metrics-port` argument for the Metrics Adapter) at `/metrics`.  The metrics collected in the Metrics Adapter are only active when the HPA is active (> 0 replicas).
 
 The following metrics are being gathered:

content/docs/2.6/operate/prometheus.md

@@ -6,6 +6,14 @@ weight = 200
 
 ## Prometheus Exporter Metrics
 
+### Operator 
+
+The KEDA Operator exposes Prometheus metrics which can be scraped on port `8080` at `/metrics`. The following metrics are being gathered:
+
+- Metrics exposed by the `Operator SDK` framework as explained [here](https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#metrics).
+
+### Metrics Adapter
+
 The KEDA Metrics Adapter exposes Prometheus metrics which can be scraped on port `9022` (this can be changed by setting the `metrics-port` argument for the Metrics Adapter) at `/metrics`.  The metrics collected in the Metrics Adapter are only active when the HPA is active (> 0 replicas).
 
 The following metrics are being gathered:

content/docs/2.7/operate/prometheus.md

@@ -6,6 +6,14 @@ weight = 200
 
 ## Prometheus Exporter Metrics
 
+### Operator 
+
+The KEDA Operator exposes Prometheus metrics which can be scraped on port `8080` at `/metrics`. The following metrics are being gathered:
+
+- Metrics exposed by the `Operator SDK` framework as explained [here](https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#metrics).
+
+### Metrics Adapter
+
 The KEDA Metrics Adapter exposes Prometheus metrics which can be scraped on port `9022` (this can be changed by setting the `metrics-port` argument for the Metrics Adapter) at `/metrics`.  The metrics collected in the Metrics Adapter are only active when the HPA is active (> 0 replicas).
 
 The following metrics are being gathered:

content/docs/2.8/operate/prometheus.md

@@ -6,6 +6,14 @@ weight = 200
 
 ## Prometheus Exporter Metrics
 
+### Operator 
+
+The KEDA Operator exposes Prometheus metrics which can be scraped on port `8080` at `/metrics`. The following metrics are being gathered:
+
+- Metrics exposed by the `Operator SDK` framework as explained [here](https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#metrics).
+
+### Metrics Adapter
+
 The KEDA Metrics Adapter exposes Prometheus metrics which can be scraped on port `9022` (this can be changed by setting the `metrics-port` argument for the Metrics Adapter) at `/metrics`.  The metrics collected in the Metrics Adapter are only active when the HPA is active (> 0 replicas).
 
 The following metrics are being gathered:

content/docs/2.9/operate/prometheus.md

@@ -6,6 +6,15 @@ weight = 200
 
 ## Prometheus Exporter Metrics
 
+### Operator 
+
+The KEDA Operator exposes Prometheus metrics which can be scraped on port `8080` at `/metrics`. The following metrics are being gathered:
+
+- `keda_operator_trigger_totals` - Total number of triggers per trigger type.
+- Metrics exposed by the `Operator SDK` framework as explained [here](https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#metrics).
+
+### Metrics Adapter
+
 The KEDA Metrics Adapter exposes Prometheus metrics which can be scraped on port `9022` (this can be changed by setting the `metrics-port` argument for the Metrics Adapter) at `/metrics`.  The metrics collected in the Metrics Adapter are only active when the HPA is active (> 0 replicas).
 
 The following metrics are being gathered: