Expand scrape_config_files in the /config web UI endpoint

Proposal

Being able to quickly see the running configuration on a Prometheus instance using the /config UI endpoint is a really convenient feature of Prometheus. However, with the recent addition of being able to separate scrape configs into multiple files with scrape_config_files, you lose the ability to see exactly what the full running config actually is when using it. This can make it more difficult to easily see what relabeling is happening on individual scrape jobs.

Instead, you just see which paths are being included in the main config file, like so:

I'd propose that the contents in the /config endpoint be expanded to show the contents of the included scrape_config_files.

In order to do so, I'm not sure if the best way would be to just include it in the box that is there now or create a new section named something like "Running Configuration" that has all of the scrape config files expanded. Or to create a new endpoint entirely just for scrape configs, similar to /rules.

Regardless, I believe it's an important feature and wanted to put this out there for ideas and tracking.