Depend on external charts for PostgreSQL and Clickhouse

[maxboone]

Currently this chart schedules PostgreSQL and ClickHouse internally. However, development on the chart can be more focused on deploying uptrace itself rather than the databases behind it when maintenance of the database charts is outsourced.

For example, we could use the helm charts from bitnami for this. Doing this also enforces best practices, automatically resolving issues like #22.

I'll take a shot at this for a PR, but it will likely result in (major) breaking changes to the chart - so it might be preferred to put that into a new chart and deprecate this one.

[vmihailenco]

Agreed, a PR would be welcome 👍

You can already disable built-in ClickHouse database like this:

clickhouse:
  enabled: false

Should be the same for PostgresQL.