Solr metrics can be collected from solr clouds/standalone solr both residing within the kubernetes cluster and outside. To use the Prometheus exporter, the easiest thing to do is just provide a reference to a Solr instance. That can be any of the following:
You can also provide a custom Prometheus Exporter config, Solr version, and exporter options as described in the Solr ref-guide.
Note that a few of the official Solr docker images do not enable the Prometheus Exporter. Versions 6.6 - 7.x and 8.2 - master should have the exporter available.