Adds CouchDB scaler docs (kedacore#967)

* added couchdb docs

Signed-off-by: 26tanishabanik <26tanishabanik@gmail.com>

* added connection string

Signed-off-by: 26tanishabanik <26tanishabanik@gmail.com>

* fixed host name

Signed-off-by: 26tanishabanik <26tanishabanik@gmail.com>

Signed-off-by: 26tanishabanik <26tanishabanik@gmail.com>

content/docs/2.9/scalers/couchdb.md

@@ -0,0 +1,90 @@
++++
+title = "CouchDB"
+availability = "v2.9+"
+maintainer = "Community"
+description = "Scale applications based on CouchDB query results."
+go_file = "couchdb_scaler"
++++
+
+### Trigger Specification
+
+This specification describes the `couchdb` trigger that scales based on the outputs of a CouchDB query.
+
+```yaml
+triggers:
+- type: couchdb
+  metadata:
+    connectionString: "http://admin:password@test-release-svc-couchdb.couchdb-test-ns.svc.cluster.local:5984/"
+    host: "test-release-svc-couchdb.couchdb-test-ns.svc.cluster.local"   
+    port: "5984" 
+    dbName: "animals" 
+    queryValue: "1" 
+    query: '{ "selector": { "feet": { "$gt": 0 } }, "fields": ["_id", "feet", "greeting"] }'
+    activationQueryValue: "1"
+```
+
+**Parameter list:**
+
+- `host` - The hostname for connecting to the CouchDB service.
+- `dbName` - Name of the database.
+- `queryValue` - A threshold that will define when scaling should occur.
+- `port` - The port number of the CouchDB service.
+- `query` - A CouchDB query that should return single numeric value.
+- `activationQueryValue` - Target value for activating the scaler. Learn more about activation [here](./../concepts/scaling-deployments.md#activating-and-scaling-thresholds).(Default: `0`, Optional)
+- `connectionString` - Connection string for CouchDB database.
+
+### Authentication Parameters
+
+You can authenticate by using a username and password via `TriggerAuthentication` configuration.
+
+**Password Authentication:**
+
+- `password` - Password for configured user to login to the Couchdb instance.
+- `username` - Username for configured user to login to the Couchdb instance.
+
+### Example
+
+Here is an example of a couchdb scaler with Basic Authentication, where the `Secret` and `TriggerAuthentication` are defined as follows:
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: couchdb-secrets
+data:
+  username: COUCHDB_USERNAME
+  password: COUCHDB_PASSWORD
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: keda-trigger-auth-couchdb-secret
+spec:
+  secretTargetRef:
+  - parameter: password
+    name: couchdb-secrets
+    key: password
+  - parameter: username
+    name: couchdb-secrets
+    key: username
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name: couchdb-scaledobject
+spec:
+  scaleTargetRef:
+    name: nginx-deployment
+  triggers:
+  - type: couchdb
+    metadata:
+      hostname: "test-release-svc-couchdb.couchdb-test-ns.svc.cluster.local"
+      port: "5984"
+      dbName: "animals"
+      queryValue: "1"
+      query: '{ "selector": { "feet": { "$gt": 0 } }, "fields": ["_id", "feet", "greeting"] }'
+      activationQueryValue: "1"
+      metricName: "global-metric"
+    authenticationRef:
+      name: keda-trigger-auth-couchdb-secret
+```