Introduce Project Groups endpoint (#321)

sections/project_groups.md

@@ -0,0 +1,82 @@
+---
+layout: default
+parent: Projects
+grand_parent: Entities
+---
+
+# Project Group
+
+German: "Projektgruppen"
+
+- TOC
+{:toc}
+
+## Attributes
+
+The project group representation contains, among the standard fields, also:
+
+- projects
+- company
+- user
+
+```json
+{
+  "id": 234,
+  "name": "Project Group Name",
+  "user": {
+    "id": 933613686,
+    "firstname": "Jane",
+    "lastname": "Doe"
+  },
+  "company": {
+    "id": 760553185,
+    "name": "Acme Inc."
+  },
+  "budget": 42000.0,
+  "currency": "EUR",
+  "info": "An info text",
+  "custom_properties": {},
+  "customer_report_url": "https://mycompany.mocoapp.com/project_groups/961779869/customer_report/1142853e926ee7c4dd7e",
+  "projects": [
+    {
+      "id": 944958556,
+      "identifier": "P1234",
+      "name": "Project Name",
+      "active": true,
+      "budget": 10000.0
+    }
+  ],
+  "created_at": "2024-08-16T08:36:44Z",
+  "updated_at": "2024-08-16T08:36:44Z"
+}
+```
+
+## GET /projects/groups
+
+Retrieve all projects:
+
+```bash
+curl -X GET \
+  'https://{domain}.mocoapp.com/api/v1/projects/groups' \
+  -H 'Authorization: Token token=YOUR_API_KEY'
+```
+
+This returns an array with complete project group information (see Attributes).
+
+The following parameters can be supplied:
+
+- [Global filters apply](../entities#global-filters)
+- **user_id** – 123456
+- **company_id** – 123456
+
+## GET /projects/groups/{id}
+
+Retrieve a single project group:
+
+```bash
+curl -X GET \
+  'https://{domain}.mocoapp.com/api/v1/projects/groups/{id}' \
+  -H 'Authorization: Token token=YOUR_API_KEY'
+```
+
+This returns a single project group representation.