message: Update A2A UML: describe add_identity step
diff: @@ -30,6 +30,11 @@ RA -> RL: <b>2. indy_agent_listen
  RL -> RS: Start listening
  RL -> RA: Listener handle (cb)
  +RA -> RL: <b>3. indy_add_identity \ncan be performed multiply times for same listener and different DID
  +RL -> RW: Check my_did in wallet
  +RL -> RL: Start accepting incomming connections for the DID
  +RL -> RA: Add identity result (cb)
  +
  === Establish connection ==
  SA -> SL: <b>3. indy_create_and_store_my_did
  