feat: notify on workspace update (#15979)

Relates to https://github.com/coder/coder/issues/15845

When the `/workspace/<name>/builds` endpoint is hit, we check if the
requested template version is different to the previously used template
version. If these values differ, we can assume that the workspace has
been manually updated and send the appropriate notification. Automatic
updates happen in the lifecycle executor and bypasses this endpoint
entirely.

coderd/notifications/notifications_test.go

@@ -1048,6 +1048,22 @@ func TestNotificationTemplates_Golden(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "TemplateWorkspaceManuallyUpdated",
+			id:   notifications.TemplateWorkspaceManuallyUpdated,
+			payload: types.MessagePayload{
+				UserName:     "Bobby",
+				UserEmail:    "bobby@coder.com",
+				UserUsername: "bobby",
+				Labels: map[string]string{
+					"organization": "bobby-organization",
+					"initiator":    "bobby",
+					"workspace":    "bobby-workspace",
+					"template":     "bobby-template",
+					"version":      "alpha",
+				},
+			},
+		},
 	}
 
 	// We must have a test case for every notification_template. This is enforced below: