flvdemux: Handle the encoder metadata the same as metadatacreator

And store it in our ENCODER tag.
8 jobs for flvmux-encoder-metadata in 17 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #79351
gst indent

00:00:32

passed #79350
manifest

00:00:37

 
  Build
passed #79352
build fedora x86_64

00:03:24

 
  Test
passed #79353
check fedora

00:03:44

 
  Full Builds
passed #79354
build android arm64 api28

00:05:24

passed #79356
build cerbero cross win32

00:09:06

passed #79357
build cerbero cross win64

00:09:15

passed #79355
build cerbero fedora x86_64

00:09:21