Draft: Build libtgowt, libtgvoip and tgcalls

To my current understanding, the telgram call stack consists of:

• libtgowt
• libtgvoip
• tgcalls

Building these is pretty straight forward in Ubuntu 22.10, because all dependencies are available in a compatible version (see !449).

This MR tries provide 20.04 based build configs. The struggle is with building the dependencies of the three libs.

• abseil (does not cross compile because of https://github.com/abseil/abseil-cpp/issues/1241)
• vpx: 1.8 in 20.04, bu 1.10 required. Building from sources failed with Fatal error: invalid -march= option: armv7-a for armhf.
• ...