Various changes to support building from upstream sources

- The pkgrel doesn't make much sense when building for upstream as
  it will never change so omit it from the version tags. This also
  allows us to start using the date for the version tag to ensure
  any package we build from upstream always has a higher version than
  previous builds without triggering unnecessary rebuilds (changing
  version-tag triggers rebuilds of many meson targets as they depend
  on the version tag).
- Add libarchive dependency when building for upstream as the
  libarchive was added as an optional dependency in
  https://github.com/systemd/systemd/pull/31075 so when we're building
  for upstream let's pull it in as a dependency.
- Add support for setting QUIET=1 which allows configuring verbose or
  quiet meson operation with the QUIET environment variable.
- Allow specifying extra meson configure options via an environment variable
- Build in developer mode when UPSTREAM=1. This enables some experimental
  components such as systemd-vmspawn and enables various options that are
  useful for debugging.