[TTAHUB-35]: Add a bit of API documentation for download endpoint

docs/openapi/paths/activity-reports/download.yaml

@@ -0,0 +1,40 @@
+get:
+  tags:
+    - activity-reports
+  summary: Download activity reports, in various formats.
+  description: >-
+    Multiple report ids can be selected by repeat use of the `report` parameter.
+  parameters:
+    - name: report
+      in: query
+      description: Ids of reports to include in download
+      required: true
+      style: form
+      schema:
+        type: array
+        minItems: 1
+        items:
+          type: integer
+    - name: format
+      in: query
+      description: Format to download report in
+      required: false
+      style: form
+      schema:
+        type: string
+        enum:
+          - json
+          - csv
+        default: json
+
+  responses:
+    200:
+      description: Successfully retrieved activity reports
+      content:
+        text/csv; charset=utf-8:
+          schema:
+            type: string
+        application/json:
+          schema:
+            type: object
+            $ref: '../../index.yaml#/components/schemas/activityReport'

docs/openapi/paths/index.yaml

@@ -14,6 +14,8 @@
   $ref: './adminAllUsers.yaml'
 '/activity-reports':
   $ref: './activity-reports/activity-reports.yaml'
+'/activity-reports/download':
+  $ref: './activity-reports/download.yaml'
 '/activity-reports/goals':
   $ref: './activity-reports/goals.yaml'
 '/activity-reports/approvers':