Add mechanism for overriding all DWO configuration per-namespace

[amisevsk]

Description

In some cases, it would be convenient to be able to configure DWO from another operator. For example, the Eclipse Che Operator depends on DWO and has its own configuration. To avoid a situation where a user has to configure Eclipse Che and DWO separately, it would be convenient if there as a mechanism to add a DevWorkspaceOperatorConfig to a namespace to configure workspaces in that namespace.

For example, configuring storage in Eclipse Che currently requires

1. Setting up the Che Operator to use a specific storage class (e.g. common)
2. Updating DWO config to set default PVC size for that storage class.

Instead, both fields could be configured in the Che Operator. For fields controlled by DWO, Che would then create a DWOC that DWO reads to override its internal configuration.

This would also have the benefit of allowing DevWorkspaces used for Che to be configured separately from other workspaces (e.g. Web Terminals or manually-created DevWorkspaces)

Additional context

[amisevsk]

Fixed by #918