Generate GStreamer Registry on build

[azubieta]

GStreamer Registry build consumes a huge amount of time and resources when the applications are launched. Such effort can be saved if it's created at build time.

It could be done as follows:

• set .env GST_REGISTRY=$APPDIR/usr/lib/arm-linux-gnueabihf/gstreamer-1.0/registry.bin to a path inside the bundle
• start the application to trigger the cache generation
• set GST_REGISTRY_UPDATE=no to prevent the regeneration on further runs

Reference: https://gstreamer.freedesktop.org/documentation/gstreamer/running.html?gi-language=c