Adjust Thanos settings

* Reduce the thanos store allocated memory percent to avoid OOMing for large queries.
* Enable default automatic downsampled data for Grafana requests.
2 jobs for <span class="ref-name">bjk/thanos_query_cache_math</span> in 3 minutes and 21 seconds (queued for 21 seconds)
Status Job ID Name Coverage
  Test
passed #189683678
rspec

00:01:54

 
  Lint
passed #189683680
cookstyle

00:01:26