Compress rules, jobs for cos-proxy

[sed-i]

Issue

Some productions deployments have several megs of relation data just for alert rules, scrape jobs. Contributing factors to the high volume of reldata:

• Scrape jobs are repeated per unit per parameter.
• Alert rules are replicated per unit.

As a result, every event cos-proxy gets from nrpe relation-changed, results in reading/writing several megs of data, taking several seconds to complete. When many units are at play, model settling takes a long time.

In addition, relation data limit is 16M, and in common envs we already approach 25% of that.

Solution

• LZMA-compress rules, jobs before storing in reldata, but only in MetricsEndpointAggregator.
• Decode in MetricsEndpointConsumer.
• Use encode/decode methods from grafana.

TODO:

• Since we're bumping LIBAPI here, could consider addressing some of the TODO/FIXMEs sprinkled in the code.

Context

• https://github.com/canonical/cos-proxy-operator/issues/56
• https://github.com/canonical/cos-proxy-operator/pull/139

Testing Instructions

Upgrade Notes

[sed-i]

As of writing, the diff between v0 and v1 is: