HelmChart: enable dependency manager to use the in memory cache

[souleb]

This PR:

• enables a chartRepository to strategically load an Index from a memory cache
• provide cache events metrics

Tests

With cache enabled

for the case we used the following flags

     spec:
       containers:
       - args:
         - --helm-cache-purge-interval=10m
         - --helm-cache-ttl=1h
         - --helm-cache-max-size=10
         - --events-addr=http://notification-controller.flux-system.svc.cluster.local./
         - --watch-all-namespaces=true
         - --log-level=info
         - --log-encoding=json
         - --enable-leader-election
         - --storage-path=/data
         - --storage-adv-addr=source-controller.$(RUNTIME_NAMESPACE).svc.cluster.local.

We have 2 HelmRepositories:

• Bitnami (interval 10m), 12.8 MB, with 10 running Helmrelease (interval 1m)
• Prometheus-Stack(Interval 10M), with 1 running HelmRelease (interval 1m)

After 1h, we have gathered the followiing information from grafana

the metric query for HitRate is sum(rate(gotk_cache_events_total{event_type="cache_hit"}[1m]))/sum(rate(gotk_cache_events_total[1m]))

With cache disabled

Signed-off-by: Soule BA soule@weave.works

[hiddeco]

Thank you very much for following up on this @souleb. 💯