vhost-device-sound: Add GStreamer audio backend support

[nicholasdezai]

Summary of the PR

This change adds GStreamer audio backend support.

Since the Rust bindings for GStreamer rely on the underlying C libraries, this change introduces additional build dependencies. On Debian/Ubuntu systems, at least libgstreamer1.0-dev and libgstreamer-plugins-base1.0-dev are required.

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[dorindabassey]

the build is failing because gstreamer-base-1.0 is missing from the build environment, looks like we need to update the rust-vmm container with gstreamer.

  pkg-config exited with status code 1
  > PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 pkg-config --libs --cflags gstreamer-base-1.0 'gstreamer-base-1.0 >= 1.20'
  The system library `gstreamer-base-1.0` required by crate `gstreamer-base-sys` was not found.
  The file `gstreamer-base-1.0.pc` needs to be installed and the PKG_CONFIG_PATH environment variable must contain its parent directory.
  The PKG_CONFIG_PATH environment variable is not set.

[MatiasVara]

the build is failing because gstreamer-base-1.0 is missing from the build environment, looks like we need to update the rust-vmm container with gstreamer.

  pkg-config exited with status code 1
  > PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 pkg-config --libs --cflags gstreamer-base-1.0 'gstreamer-base-1.0 >= 1.20'
  The system library `gstreamer-base-1.0` required by crate `gstreamer-base-sys` was not found.
  The file `gstreamer-base-1.0.pc` needs to be installed and the PKG_CONFIG_PATH environment variable must contain its parent directory.
  The PKG_CONFIG_PATH environment variable is not set.

right, I just did it at rust-vmm/rust-vmm-ci#190

[stefano-garzarella]

@nicholasdezai we just merged #881 that should bring @MatiasVara changes to add GStreamer deps to our CI container, please rebase this PR.

[nicholasdezai]

I submitted a PR to rust-vmm-container to add the missing GStreamer dependencies
(gstreamer1.0-plugins-base and gstreamer1.0-plugins-good) required for running
the GStreamer backend tests in CI.