Use newer OCI labels in Dockerfile

[Mr0grog]

Our current Dockerfile uses the maintainer label:

web-monitoring-diff/Dockerfile

Lines 9 to 10 in 0f54fd6

	FROM python:3.10.7-slim as base
	LABEL maintainer="enviroDGI@gmail.com"

Which has been deprecated in favor of a new, standardized org.opencontainers.image.authors label. In fact, there is a whole list of OCI-standardized labels that are supported by various tools (e.g. Dependabot now uses org.opencontainers.image.source to figure out release notes and so on) that we should be using: https://github.com/opencontainers/image-spec/blob/main/annotations.md#pre-defined-annotation-keys