feat(core): include initiationMethod in conversation interaction telemetry (#22054)

Co-authored-by: Yuna Seol <yunaseol@google.com>

packages/core/src/code_assist/telemetry.test.ts

@@ -339,6 +339,7 @@ describe('telemetry', () => {
           acceptedLines: '8',
           removedLines: '3',
           isAgentic: true,
+          initiationMethod: InitiationMethod.COMMAND,
         }),
       );
     });