decproxy: add mime-type in media-info
decproxy: add mime-type in media-info

:issues addressed:
[BHV-13632] Add missing field in media-info

Change-Id: I6d1c559dfcf4761cfbcb8e237e47a13786b738f4
Reviewed-on: https://gpro.lgsvl.com/61911
Reviewed-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>
Tested-by: Jeongseok Kim <0c03ab7a1b32f29697716389c3f9549845834271@lge.com>

justinjoy/gst-plugins-cool,justinjoy/gst-plugins-cool