Github releases for CI

From: Peter Dimov (pdimov_at_[hidden])
Date: 2024-03-14 00:39:01

In addition to the CMake releases on Github, I've modified
the action to also create releases for use with b2 (with the
headers copied to boost/ and removed from libs/*/include,
but without the documentation.)

These would be useful for CI, which would hopefully lower
the pressure on the official downloads.

E.g. https://github.com/boostorg/boost/releases/tag/boost-1.85.0.beta1