Allow users to specify Jetty options

The solrcloud CRD and accompanying helm chart offer ways to set most common `bin/solr` options, but I recently ran into one of the few exceptions: Jetty options/arguments. As far as I know there's no way to customize the arguments passed to Jetty in a solrcloud, outside of baking certain options into the Docker image itself.

We should find a way to support this usecase. Two initial approaches come to mind:

1. Allow users to override the Docker "command" more broadly. (At which point they can rely on the Solr CLI's `-j` option)
2. Expose a CRD setting specific to Jetty options that then gets inserted into a Docker "command" template.

Start with the solrcloud CRD and accompanying Helm chart, then trace how bin/solr options become the Docker command. Compare the two proposed approaches—broader command overrides or a Jetty-specific CRD setting using Solr CLI's -j option—and establish the supported configuration and its completion criteria.

Written by the indexing model from the issue text.