Show also original labels for duplicate targets in error message in order to simplify debugging the issue.
Now `/targets` endpoint accepts optional `show_original_labels=1` query arg, which shows original labels for each target.
This may simplify debugging for target relabeling.
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/651
The change to `vm_promscrape_targets` metric suppose to improve observability
for `vmagent` so it will be possible to track how many targets are up or down
for every specific scrape group:
```
vm_promscrape_targets{type="static_configs", status="down"} 1
vm_promscrape_targets{type="static_configs", status="up"} 2
```
This is a common error whith improperly configured target autodiscovery and/or relabeling.
This error leads to duplicate scraping of the same targets with the same set of labels, which leads
to duplicate samples in time series.
Previously targets with duplicate scrape urls were merged into a single line on the page.
Now each target with duplicate scrape url is displayed on a separate line.
