Update Loki endpoint and json format

[sboschman]

Motivation

Currently falcosidekick uses the deprecated Loki /api/prom/push endpoint (https://grafana.com/docs/loki/v2.6.x/api/#post-apiprompush). Might be a good idea to switch to the new Loki /loki/api/vi/push endpoint (https://grafana.com/docs/loki/v2.6.x/api/#push-log-entries-to-loki), including the new json format, before the old endpoint is dropped.

Feature

Switch Loki endpoint and json message format to the /loki/api/v1/push endpoint. I believe this endpoint has been available since Loki v1.0.0. Anyways, the oldest documentation on the site is for v1.6.x (https://grafana.com/docs/loki/v1.6.x/api/#post-lokiapiv1push), which has the endpoint. Loki v1.6.0 was released on 13 Aug 2020, so imho support for the old endpoint can just be dropped.

Alternatives

Assume Loki never drops this deprecated endpoint 😨

Additional context

[Issif]

Hi,

The PR #309 introduced the possibility to set the URI for Loki endpoint, I agree it's time to use /loki/api/v1/push as default and the JSON format (much easier to debug). For avoiding to break things for users with old Loki servers, I'll add a option to choose the event format, just in case.

[Issif]

I finally decided to deprecate the old format for the new one, as it's there for a while. It seems to be ok in my last tests:

[Issif]

It will be released with next version 👍