chore: generate a schema for keycloak helm chart (#627)

## Description

Using [remarshal](https://github.com/remarshal-project/remarshal) and
[generate-json-schema](https://github.com/Nijikokun/generate-schema), I
locally created a `values.schema.json` file for keycloak's chart. I also
referenced [this
post](https://www.arthurkoziel.com/validate-helm-chart-values-with-json-schemas/)
to build context on schemas & helm charts.

## Related Issue

Fixes #563 

## Type of change

- [X] Other (security config, docs update, etc)

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [x] [Contributor
Guide](https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md)
followed

---------

Co-authored-by: Micah Nagel <micah.nagel@defenseunicorns.com>
Co-authored-by: Chance <139784371+UnicornChance@users.noreply.github.com>