Add deprecation warning to inject

src/dodal/common/coordination.py

@@ -1,4 +1,6 @@
 import uuid
+import warnings
+from textwrap import dedent
 from typing import Any
 
 from dodal.common.types import Group
@@ -37,4 +39,20 @@ def scan(x: Movable = inject("stage_x"), start: float = 0.0 ...)
 
     """
 
+    warnings.warn(
+        dedent("""
+        Inject is deprecated, users are now expected to call the device factory 
+        functions in dodal directly, these will cache devices as singletons after
+        they have been called once. For example:
+
+        import i22
+
+        + def my_plan(detector: Readable = i22.saxs()) -> MsgGenerator:
+            ...
+
+        Where previously the default would have been inject("saxs")
+        """),
+        DeprecationWarning,
+        stacklevel=2,
+    )
     return name