Upgrade the helm chart with subcharts to make it more versatile

**Is your feature request related to a problem? Please describe.**
Currently the helm chart is in an MVP state, where we setup a minimum mongo, redis and checkmate deployment. It allows very little in the ways of customization.

**Describe the solution you'd like**
Instead of defining resources directly in our templates, we would override them using standard sub-charts.

Mongodb -> bitnami/mongodb
Redis -> bitnami/redis
Checkmate itself -> bjw-s-labs/app-template

We should also be able to turn off components in order to deploy them ourselves (for example with `mongodb.enabled: false`)

**Additional context**
This feature needs to also update the documentation to reflect the new charts and their values and how to configure them.

Locate the current Helm chart templates and values first, then compare their MongoDB, Redis, and Checkmate resources with the requested Bitnami and bjw-s-labs/app-template subcharts. The work is complete when the subcharts and their values support customization, each component can be disabled, and the documentation explains the available charts, values, and configuration.

Written by the indexing model from the issue text.