docs: Update API documentation

- Add /api prefix to all endpoint documentation
- Document the new /api/health endpoint in README and OpenAPI spec

Author: mantono

API/README.md

@@ -8,15 +8,18 @@ Requests that may change the state (PUT & DELETE) will require authenticaiton if
 In such case the authorization header must be sent with the proper API key.
 Example: `authorization: ApiKey SECRET_API_KEY`
 
-## GET `/flags/{namespace}`
+## GET `/api/flags/{namespace}`
 Get all the enabled feature flags in a namespace.
 
-## HEAD `/flags/{namespace}`
+## HEAD `/api/flags/{namespace}`
 Check if the feature flags have been updated for a namespace. The response will contain the [etag](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag) header.
 If the etag header value is the same as in the most recent GET or HEAD request, the namespace's feature flags have not changed.
 
-## PUT `/flags/{namespace}/{flag}`
+## PUT `/api/flags/{namespace}/{flag}`
 Enable a feature flag in a namespace.
 
-## DELETE `/flags/{namespace}/{flag}`
-Disable a feature flag in a namespace.
+## DELETE `/api/flags/{namespace}/{flag}`
+Disable a feature flag in a namespace.
+
+## GET `/api/health`
+Health check endpoint that can be used to verify the service is running in a healthy state.

open_api.yaml

@@ -80,6 +80,16 @@ paths:
         '401':
           description: Unauthorized
 
+  /api/health:
+    get:
+      summary: Health check endpoint
+      description: Check the health status of the service and its database connection (if any)
+      responses:
+        '200':
+          description: Service is healthy
+        '503':
+          description: Service is unavailable
+
 components:
   schemas:
     Response: