Catch when two targets are relabelled to the same labels

[gouthamve]

When two different targets end up with the same labels after relabelling, two scrape loops are created and OOO ingestion errors are logged.

We should ideally catch this and log it. And create only one scrape loop per target labelset.

This might break some setups as people might be abusing it already and are safe if the two targets don't have any common metrics.

[roidelapluie]

I would rather not scrape the targets than creating just one scrape config, as two instances can get the same labelset if you overwrite the metrics.

Also, we can have the issue with honor_label: true anyway ..

[brian-brazil]

This is about target labels rather than scraped labels.

And create only one scrape loop per target labelset.

I don't think that'll be practical, which one would you choose?