plugins.dash: add support for parameters
plugins.dash: add support for parameters

This allows passing parameters to `DASHStream` and `requests.request`,
similar to the HLS protocol plugin. See `DASHStream.parse_manifest`.

chhe/streamlink,gravyboat/streamlink,bastimeyer/streamlink,gravyboat/streamlink,streamlink/streamlink,bastimeyer/streamlink,streamlink/streamlink,chhe/streamlink