Added libgl1-mesa-dev as a dependency to debian/control

[nielsreijers]

Similar to PR 3471

I tried building multipass in a clean 22.04 vm (started using multipass) following the instructions in the README.md.

This failed on the cmake ../ step:

-- Could NOT find OpenGL (missing: OPENGL_INCLUDE_DIR) 
-- Could NOT find WrapOpenGL (missing: WrapOpenGL_FOUND) 
CMake Warning at 3rd-party/vcpkg/scripts/buildsystems/vcpkg.cmake:855 (_find_package):
  Found package configuration file:

    /usr/lib/x86_64-linux-gnu/cmake/Qt6Gui/Qt6GuiConfig.cmake

  but it set Qt6Gui_FOUND to FALSE so package "Qt6Gui" is considered to be
  NOT FOUND.  Reason given by package:

  Qt6Gui could not be found because dependency WrapOpenGL could not be found.

This in turns causes Qt6Widgets and Qt6 to be NOT FOUND and the script to fail.

Adding libgl1-mesa-dev fixes this.

[townsend2010]

Hey @nielsreijers!

Thanks for this contribution! Just as you add this, we will be removing the dependency on Qt6Widgets/Qt6Gui very soon in #3282. That said, I don't think this will be relevant anymore once that is merged. I'll leave this open for now just in case this is actually still needed once we merge that other PR.