feat: add some documentation

ee/ingester/Earthfile

@@ -140,4 +140,11 @@ generate-sdk:
         -p packageName=ingesterclient
     RUN rm -rf ./client/test
     RUN ls -lisah
-    SAVE ARTIFACT ./client AS LOCAL pkg/client
+    SAVE ARTIFACT ./client AS LOCAL pkg/client
+
+openapi-doc:
+    FROM node:22-alpine
+    RUN npm install -g widdershins
+    COPY api/openapi.yaml .
+    RUN widdershins openapi.yaml --search false --language_tabs 'http:HTTP' -o openapi.md --omitHeader --summary --code --httpsnippet
+    SAVE ARTIFACT openapi.md AS LOCAL api/openapi.md

ee/ingester/README.md

@@ -1,5 +1,31 @@
 # Ingester
 
+This component is dedicated to data ingestion on Formance modules.
+It allows to create connectors (elasticsearch, clickhouse, ...), and create pipelines, plugging modules (ledger, payments...) on them.
+
+# Modules requirements
+
+The components must follow some guidelines to be able to be integrated with the ingester.
+Each must : 
+* have a /logs endpoint returning past logs in a normalized format
+  > **_NOTE:_**  The endpoint must also support the cursors.
+* push logs in a topic named `<stack>.<module name>` on the stack broker
+
+The log is a json object containing following properties:
+
+| Name | Description                       | Type | Required |
+|-|-----------------------------------|-|-|
+| id | The log id                        | string or bigint | Yes |
+| date | The log date                      | string / rfc3339 | Yes |
+| type | The log type. Defined by modules. | string | Yes |
+| payload | The log payload. | object | Yes |
+| shard | The log shard. Can be used to split data of the modules using modules business rules | Yes |
+
+
+> **_NOTE:_**  The `shard` property allow to split logs of a modules. 
+> The format of the field is defined by the modules and can be empty if not required.
+> However, it must not be greater than 256 characters.
+
 ## Pipeline state diagram
 
 ```mermaid
@@ -10,4 +36,8 @@ stateDiagram-v2
     if_state --> FetchData: if state == INIT
     FetchData --> ProcessEvents: All data initialized.\nSwitch to state READY
     ProcessEvents --> FetchData: Reset triggered.\nSwitch to state INIT
-```
+```
+
+## API Spec
+
+See [Spec](./api/openapi.md)