feat: add observability plugin system (#227)

Co-authored-by: Michael Neale <michael.neale@gmail.com>
Co-authored-by: Lifei Zhou <lifei@squareup.com>
Co-authored-by: Alice Hau <ahau@squareup.com>

tests/test_profile.py

@@ -1,4 +1,4 @@
-from goose.profile import ToolkitSpec
+from goose.profile import ToolkitSpec, ObserverSpec
 
 
 def test_profile_info(profile_factory):
@@ -7,6 +7,10 @@ def test_profile_info(profile_factory):
             "provider": "provider",
             "processor": "processor",
             "toolkits": [ToolkitSpec("developer"), ToolkitSpec("github")],
+            "observers": [ObserverSpec(name="test.plugin")],
         }
     )
-    assert profile.profile_info() == "provider:provider, processor:processor toolkits: developer, github"
+    assert (
+        profile.profile_info()
+        == "provider:provider, processor:processor toolkits: developer, github observers: test.plugin"
+    )