prometheus: add support for installing webhook server

roles/prometheus/meta/argument_specs.yml

@@ -51,6 +51,11 @@ argument_specs:
         type: bool
         required: false
         default: true
+      prometheus_install_webhook:
+        description: If true, installs webhook server in the same docker network as prometheus and configures it
+        type: bool
+        required: false
+        default: false
 
       alertmanager_storage_retention:
         description: Period of time for which alertmanager data is stored for. A number followed by unit (s, m, h, d, w, y). Passed directly to alertmanager role
@@ -58,6 +63,47 @@ argument_specs:
         required: false
         default: "{{ prometheus_storage_retention | default('3650d') }}"
 
+      prometheus_webhook_handlers:
+        description: List of webhook server handlers
+        type: list
+        required: "{{ prometheus_install_webhook }}"
+        elements: dict
+        options:
+          id:
+            description: specifies the ID of your hook. This value is used to create the HTTP endpoint
+            type: str
+            required: true
+          execute-command:
+            description: specifies the command that should be executed when the hook is triggered
+            type: str
+            required: true
+          command-working-directory:
+            description: specifies the working directory that will be used for the script when it's executed
+            type: str
+            required: false
+          pass-arguments-to-command:
+            description: >
+              specifies the list of arguments that will be passed to the
+              command. See for more info:
+              https://github.com/adnanh/webhook/blob/master/docs/Referencing-Request-Values.md
+            type: list
+            required: false
+            elements: dict
+            options:
+              source:
+                description: Source of the argument. Use `string` to specify argument here.
+                type: str
+                required: true
+                choices:
+                  - string
+                  - header
+                  - url
+                  - request
+                  - payload
+              name:
+                description: Argument if source is string, otherwise the source attribute name.
+                type: str
+                required: true
 
       # All options after this will be passed directly to the container role
       docker_service_suffix: