Specify the behaviour of the task queue once it is full (#231)

* Update 0060-tasks-api.md

* add the special error message when the task queue is full

text/0060-tasks-api.md

@@ -505,6 +505,7 @@ When the request is successful, Meilisearch returns the HTTP code 202 Accepted.
 If a user tries deleting an `enqueued`, or `processing` task, it won’t throw an error. Task deletion is an atomic transaction; all tasks are successfully deleted, or none aren't.
 
 - 🔴 Sending a task deletion without filtering query parameters returns a [missing_task_filters](0061-error-format-and-definitions.md#missing_task_filters) error.
+- 🔴 Sending a task once the task queue is full will throw a [`no_space_left_on_device`](0061-error-format-and-definitions.md#no_space_left_on_device) error. Once this state is reached, the only possible action is to delete tasks.
 
 The auth layer can return the following errors if Meilisearch is secured (a master-key is defined).
 

text/0061-error-format-and-definitions.md

@@ -2634,6 +2634,7 @@ HTTP Code: `500 Internal Server Error` when `Synchronous`
 ### Context
 
 This error occurs when the host system partition has reached its maximum capacity and no longer accepts writes.
+It can also happens when the task queue reaches its limit of ~10GiB of tasks (~10M tasks).
 
 ### Error Definition
 
@@ -2648,6 +2649,17 @@ HTTP Code: `500 Internal Server Error` when `Synchronous`
 }
 ```
 
+In the case of the task queue being full the HTTP Code returned is `422 Unprocessable Entity` when `Synchronous`.
+
+```json
+{
+    "message": "Meilisearch cannot receive write operations because the limit of the task database has been reached. Please delete tasks to continue performing write operations.",
+    "code": "no_space_left_on_device",
+    "type": "system",
+    "link": "https://docs.meilisearch.com/errors#no_space_left_on_device"
+}
+```
+
 ---
 
 ## too_many_open_files