server: Add default configuration to connect to the codeintel upload store

Created by: efritz

This adds the default variables required to connect to MinIO in the server environment and changes the variables so that they are correct for docker/k8s deployments out of the box. Only server, dev, and cloud should need to update any of these variables.

While updating values I realized that our defaults were broken (we were unable to unset some variables that enabled some non-opt-out functionality). This is now corrected.

Related documentation change: https://github.com/sourcegraph/sourcegraph/pull/15071