Add the suggested SSE protocol to the documentation

source/index.rst

@@ -13,6 +13,7 @@
    Code rules <coderules>
    Roles <roles/index>
    Services <services/index>
+   SSE Protocol <sse>
 
    License <license>
    Authors <authors>

source/sse.rst

@@ -0,0 +1,44 @@
+.. _sse:
+
+############
+SSE protocol
+############
+
+ETOS communicates to clients using SSE (server sent events). For now ETOS only sends log messages using the protocol but we are adding more data about testruns into the protocol.
+
+.. list-table:: SSE Protocol
+  :widths: 25 25 25 25
+  :header-rows: 1
+
+  * - Name
+    - Why
+    - Example
+    - State
+  * - Ping
+    - Keep the connection alive
+    - {id: None, event: Ping, data: ""}
+    - Implemented
+  * - Shutdown
+    - Server wants the client to shut down the connection
+    - {id: None, event: Shutdown, data: "ESR has shut down"}
+    - Implemented
+  * - NotFound
+    - The server cannot find the ESR instance, retry after a while
+    - {id: None, event: NotFound, data: "ESR not found"}
+    - Suggested
+  * - Error
+    - The server got an error. Retry may be possible
+    - {id: None, event: Error, data: '{"retry": bool, "reason": "Some sort of error"}}
+    - Suggested
+  * - Message
+    - A user log message from ETOS
+    - {id: 1, event: message, data: "{'message': 'a message', '@timestamp': '%Y-%m-%dT%H:%M:%S.%fZ', 'levelname': 'INFO', 'name': 'ESR'}"}
+    - Implemented
+  * - Artifact
+    - An artifact to download
+    - {id: 1, event: Artifact, data: "{'url': 'http://download.me'}"}
+    - Suggested
+  * - TestCase
+    - A test case execution
+    - {id: 1, event: TestCase, data: "{'id': 'uuid', 'triggered': True, 'started': True, 'finished': False}"}
+    - Suggested