feat: Implement conf.tasks_default_queues (#1434)

@CallDeferred tasks run in the Cloud Tasks Queue "default" by default.
One way to run them in a different task queue is to use the `_queue`
parameter when calling the task.
However, as this is not possible for existing or low-hanging calls,
default values can be defined here for each task.
To do this, the task path must be mapped to the queue name:
```
conf.tasks_default_queues["updateRelations.viur.core.skeleton"] = "update_relations"
```
The queue (in the example: `"update_relations"`) must exist. The default
queue can be changed by overwriting `"__default__"`.

src/viur/core/config.py

@@ -911,6 +911,23 @@ def tasks_custom_environment_handler(self, value: "CustomEnvironmentHandler") ->
         else:
             raise ValueError(f"Invalid type {type(value)}. Expected a CustomEnvironmentHandler object.")
 
+    tasks_default_queues: dict[str, str] = {
+        "__default__": "default",
+    }
+    """
+    @CallDeferred tasks run in the Cloud Tasks Queue "default" by default.
+    One way to run them in a different task queue is to use the `_queue` parameter
+    when calling the task.
+    However, as this is not possible for existing or low-hanging calls,
+    default values can be defined here for each task.
+    To do this, the task path must be mapped to the queue name:
+    ```
+    conf.tasks_default_queues["updateRelations.viur.core.skeleton"] = "update_relations"
+    ```
+    The queue (in the example: `"update_relations"`) must exist.
+    The default queue can be changed by overwriting `"__default__"`.
+    """
+
     valid_application_ids: list[str] = []
     """Which application-ids we're supposed to run on"""
 

src/viur/core/tasks.py

@@ -456,7 +456,9 @@ def CallDeferred(func: t.Callable) -> t.Callable:
     In addition to the arguments for the wrapped methods you can set these:
 
     _queue: Specify the queue in which the task should be pushed.
-        "default" is the default value. The queue must exist (use the queue.yaml).
+        If no value is given, the queue name set in `conf.tasks_default_queues`
+        will be used. If the config does not have a value for this task, "default"
+        is used as the default. The queue must exist (use the queue.yaml).
 
     _countdown: Specify a time in seconds after which the task should be called.
         This time is relative to the moment where the wrapped method has been called.
@@ -500,7 +502,7 @@ def make_deferred(
         func: t.Callable,
         self=__undefinedFlag_,
         *args,
-        _queue: str = "default",
+        _queue: str = None,
         _name: str | None = None,
         _call_deferred: bool = True,
         _target_version: str = conf.instance.app_version,
@@ -564,6 +566,11 @@ def task():
                     args = (self,) + args  # Re-append self to args, as this function is (hopefully) unbound
                 command = "unb"
 
+            if _queue is None:
+                _queue = conf.tasks_default_queues.get(
+                    funcPath, conf.tasks_default_queues.get("__default__", "default")
+                )
+
             # Try to preserve the important data from the current environment
             try:  # We might get called inside a warmup request without session
                 usr = current.session.get().get("user")