positions.ignore-corruptions

[owen-d]

Adds a new config, positions.ignore-corruptions which allows ignoring corrupted yaml in the positions files. I believe this is already largely mitigated by the introduction of atomic file updates to the positions file.

This flag will not affect existing deployments, which error upon startup when finding malformed positions yaml.

closes #1460

[rfratto]

LGTM, although I don't know about referring to it as a "corrupted" file, since it would apply for any invalid YAML. WDYT about changing it to ignore_invalid_yaml?

[owen-d]

I think you're right, @rfratto. I'll make the change

[pstibrany]

I don't see much need for this. If one has corrupted positions file, and promtail doesn't start, then error message now says which file is the culprit, and admin can inspect / delete it. Alternatively admin can set this flag (as it defaults to false), but has to know about it first. As you point out, promtail should not generate corrupted position file anymore.

I would prefer if we reduced number of options rather than adding new ones.