chart: Use SQLite for grafana instead of timescaledb

[paulfantom]

Description

Using SQLite would allow us to still use grafana when database is down or under high pressure.

This is a breaking change.

Fixes #338

Type of change

What type of changes does your code introduce to tobs? Put an x in the box that apply.

• CHANGE (fix or feature that would cause existing functionality to not work as expected)
• FEATURE (non-breaking change which adds functionality)
• BUGFIX (non-breaking change which fixes an issue)
• ENHANCEMENT (non-breaking change which improves existing functionality)
• NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

[paulfantom]

Note: parenthesis here allow to have each level be nullable and thus prevent issues with nil pointer evaluating interface when higher level object doesn't exist.

[paulfantom]

After merging this we are defaulting to sqlite database for grafana. Configuration for timescaledb is still present for users who upgrade from previous tobs versions, but will be removed in tobs 0.12.0.

By default upgrade will switch grafana to use sqlite3 and if user wants to stay on timescaledb backend, they need to set:

kube-prometheus-stack:
  grafana:
    timescale:
      database:
        enabled: true

[onprem]

LGTM!