Update container labels to follow the OCI spec

[patrick-stephens]

We should use the correct labels now for the various metadata in the dockerfiles, e.g. LABEL org.opencontainers.image.description DESCRIPTION

This is then also picked up automatically for Github Packages: https://github.com/fluent/fluent-bit/pkgs/container/fluent-bit/12844397?tag=1.8.11

See fluent/fluent-bit-docker-image#42 and https://github.com/opencontainers/image-spec/blob/main/annotations.md