Enable Restricted RTP/RTCP Source UDP ClientPort Ranges to facilitate MediaMTX Source UDP reception inside K8s deployments

[bjornss-scaleaq]

This is a suggested extension of MediaMTX Config / Env to allow reception of RTP/RTCP data over UDP, for containerized deployments used INSIDE K8s clusters, with K8s services (NodePorts/Loadbalancers ) to control UDP traffic.

See the accompanying PR
[(https://github.com/bluenviron/gortsplib/pull/985)]
for technical detail

The PR introduces a new Global Conf parameter / (ENV Variable) for RTSP sources:

# Source UDP RTP Client Port range
# This can be used to control RTSP Source UDP client port ranges for use e.g inside Kubernetes clusters
# Starting and ending ports should be EVEN numbers
# It defaults to the range [ 10000, 65534 ]
sourceUDPClientPortRange: [ 10000,65534 ]