devops: use `pkgconfig` to resolve dependencies

[aslushnikov]

This way sqlite and libmicrohttpd could be effortlessly installed on macos via Homebrew, and the compilation will just work.

NOTE: there's also a local sqlite installation on MacOS; to disambiguate with it, use PKG_CONFIG_PATH:

export PKG_CONFIG_PATH=/opt/homebrew/Cellar/sqlite/3.44.0/lib/pkgconfig/