Add typing and standardized labels for metrics

.gitlab/ci/build_releng.sh: Add print_package_version_metric() to generically print a version_info metric for a given package name and its description. Change create_metrics() to rename all metrics (and their labels) in accordance with new expectations in arch-release-promotion. Change the size related metrics to provide the data in bytes instead of mebibytes.

Fixes #16 (closed)