Add superadmin UI for configuring org storage

[tw4l]

Follow-up to #2093

Related to #578

Similar to org quotas and proxies, we should add a superuser-only admin UI for configuring org storage on the orgs list.

For each org, we should support:

• Adding a custom storage
• Removing a custom storage
• Seeing what storages are currently configured for an org via GET /storage
• Updating primary storage location via POST /storage to any storage option listed from /all-storages (if files are already stored on org, this will set org to read-only while migration happens)
• Updating replica storage locations via POST /storage-replicas to any storage options listed from /all-storages (any migrations happen in background jobs and don't interfere with archiving or set the org to read-only)

This might be best handled in a few different dialogs rather than all put into one. Or this could be a good opportunity to break out superadmin org configuration from the existing dialogs into a new detail page.