Performance improvements for restic-exporter

[k0ste]

Hi, here is some fight with restic cloud-native repo variant (S3) With options, that disables the restic check & restic stats queries - the duration of metrics collecting reduces grammatically

restic_scrape_duration_seconds 137.99019384384155
restic_scrape_duration_seconds 51.43253993988037

-e NO_CHECK="true" -e NO_STATS="true":

restic_scrape_duration_seconds 34.870311975479126
restic_scrape_duration_seconds 16.271262645721436

For "backup is not performed for a time" - the timestamp + meta metrics just enough

Full list of changes:

• Added EXIT_ON_ERROR env var - now is possible to control "exit_on_errors" behaviour
• Added NO_CHECK env var, now is possible not perform restic check operation
• Added NO_STATS env var, now is possible not collect per backup stats
• Added backup tag to the backup label (if tags is present)
• Code formatted via black formatter

[k0ste]

Thank you for the changes. I let you some comments. If you make the changes I will publish a release this weekend.

I was made changes and reverts, as you suggested 🙏

[ngosang]

https://github.com/ngosang/restic-exporter/releases/tag/1.2.0