Enable network support for FFmpeg

This patch configures FFmpeg with network support. This enables QtMM
to handle network source such as HTTP, HTTPS, or RTSP.
Details:
- on macOS and windows ffmpeg uses native security backend so we don't
  include openssl to the build. Additional patch for linking
  with the security backend is in QtMM commit under the same task.
- on linux we add openssl; for all CI linux platforms libssl-dev is
  installed.

Task-number: QTBUG-110708
Pick-to: 6.5
Change-Id: I80a7dfda702c4d554df3a7380aac642890a28b94
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

coin/provisioning/common/shared/ffmpeg_config_options.txt

@@ -1 +1 @@
---disable-programs --disable-doc --disable-debug --disable-network --disable-lzma --enable-pic
+--disable-programs --disable-doc --disable-debug --enable-network --disable-lzma --enable-pic

coin/provisioning/common/unix/install-ffmpeg.sh

@@ -143,6 +143,7 @@ build_ffmpeg_android() {
 }
 
 if [ "$os" == "linux" ]; then
+  ffmpeg_config_options="$ffmpeg_config_options --enable-openssl"
   build_ffmpeg
   sudo mv "$ffmpeg_source_dir/build/installed/usr/local/$ffmpeg_name" "/usr/local"
   SetEnvVar "FFMPEG_DIR" "/usr/local/$ffmpeg_name"