Optimize how App Engine generates reports and metrics

[rviscomi]

Related to #19 and HTTPArchive/httparchive.org#939, the HA website currently generates the reports from a reports.json config file that we manually maintain.

The way queries are organized in the analysis pipeline should be identical to the way metrics are organized in the HA reports. So instead of maintaining the config file manually, the HA website should automatically be kept in sync. We could do this by auto-generating the config file or dynamically discovering which reports/metrics are available. Either way, the App Engine config and server should handle the more optimized approach.

[rviscomi]

The ideal workflow I'm going for is to make it as easy as possible to add new metrics. So for example, if the 2022 JavaScript chapter team comes up with an idea for a new metric, the minimal amount of information needed to start tracking it should be the SQL and a bit of metadata. They can submit that to the analysis pipeline and the JS report would automatically pick it up and include the metric without having to manually update the config.