Add documentation, remove unused code

doc/api/alert_management_alerts.md

@@ -11,6 +11,36 @@ This is the documentation of Alert Management Alerts API.
 NOTE:
 This API is limited to metric images. For more API endpoints please refer to the [GraphQL API](graphql/reference/index.md#alertmanagementalert).
 
+## Upload metric image
+
+```plaintext
+POST /projects/:id/alert_management_alerts/:alert_iid/metric_images
+```
+
+| Attribute   | Type    | Required | Description                          |
+|-------------|---------|----------|--------------------------------------|
+| `id`        | integer/string | yes      | The ID or [URL-encoded path of the project](index.md#namespaced-path-encoding) owned by the authenticated user  |
+| `alert_iid` | integer | yes      | The internal ID of a project's alert |
+
+```shell
+curl --request POST --header "PRIVATE-TOKEN: <your_access_token>"  --form 'file=@/path/to/file.png' \
+--form 'url=http://example.com' --form 'url_text=Example website' "https://gitlab.example.com/api/v4/projects/5/alert_management_alerts/93/metric_images"
+```
+
+Example response:
+
+```json
+{
+    "id": 17,
+    "created_at": "2020-11-12T20:07:58.156Z",
+    "filename": "sample_2054",
+    "file_path": "/uploads/-/system/alert_metric_image/file/17/sample_2054.png",
+    "url": "example.com/metric",
+    "url_text": "An example metric"
+}
+```
+
+
 ## List metric images
 
 ```plaintext
@@ -48,3 +78,34 @@ Example response:
     }
 ]
 ```
+
+## Update metric image
+
+```plaintext
+PUT /projects/:id/alert_management_alerts/:alert_iid/metric_image/:image_id
+```
+
+| Attribute   | Type    | Required | Description                          |
+|-------------|---------|----------|--------------------------------------|
+| `id`        | integer/string | yes      | The ID or [URL-encoded path of the project](index.md#namespaced-path-encoding) owned by the authenticated user  |
+| `alert_iid` | integer | yes      | The internal ID of a project's alert |
+| `image_id` | integer | yes      | The ID of the image |
+| `url` | string | no      | The URL to view more metric information |
+| `url_text` | string | no      | A description of the image or URL |
+
+```shell
+curl --header "PRIVATE-TOKEN: <your_access_token>" --request PUT  --form 'url=http://example.com' --form 'url_text=Example website' "https://gitlab.example.com/api/v4/projects/5/alert_management_alerts/93/metric_images/1"
+```
+
+Example response:
+
+```json
+{
+    "id": 23,
+    "created_at": "2020-11-13T00:06:18.084Z",
+    "filename": "file.png",
+    "file_path": "/uploads/-/system/alert_metric_image/file/23/file.png",
+    "url": "http://example.com",
+    "url_text": "Example website"
+}
+```

ee/app/services/alert_management/metric_images/upload_service.rb

@@ -3,13 +3,12 @@
 module AlertManagement
   module MetricImages
     class UploadService < BaseService
-      attr_reader :alert, :project, :file, :url, :url_text, :metric
+      attr_reader :alert, :file, :url, :url_text, :metric
 
       def initialize(alert, current_user, params = {})
         super
 
         @alert = alert
-        @project = alert&.project
         @file = params.fetch(:file)
         @url = params.fetch(:url, nil)
         @url_text = params.fetch(:url_text, nil)