kmswebrtcendpoint: autogenerate certkey PEM file when needed

Change-Id: I9c8239c105c83627f80d9f59210ad521db5579b0
webrtc_http_server: fix main loop creation

Change-Id: I50e9dd87722c0ff3595db41501e5b34c78a9dab1
webrtc_http_server: use kms_element_link_pads

Change-Id: Ib44d1b7e38821090a4427e815ffcd2f77f76c83e
webrtc_http_server: add audio support

Change-Id: Ica0535338a1ce2b10ec5596ef8bc07302995c79f