Switch to multi-stage build

This simplifies the build pipeline, as no "cleanup" stage has to be
done, and allow precise description of the runtime libraries required
to use Valkey.

The result reduces Debian (uncompressed) image size from 140MB to 116MB
(a 17% improvement), and allow certain tools like wget to be removed
from the build by using native `ADD` instructions. The number of
vulnerabilities (as reported by trivy) in the Debian image also drops
from 693 to 77, where the main contributors are left-over build
dependencies.

The Alpine image did not see any improvement, however.

Signed-off-by: Leorize <leorize+oss@disroot.org>

Author: alaviss