Update ImsCallingTest with remotely hosted conference testing.

This CL adds CTS test for both the legacy addConference path and the new addConferenceFromConnection path for adding a remotely hosted conference in Telecom.

Test: atest ImsCallingTest
Flag: com.android.internal.telephony.flags.reuse_original_conn_remote_conf_behavior
Bug: 391889544
Change-Id: I54d7b4add2e7664d8cdb0bcc1d874086c8dcdef0