Provide read-only view of dmn modeler with overview plugin

[SebastianStamm]

Is your feature request related to a problem? Please describe.

With #2 we implemented an overview feature that provides users with the ability to quickly switch between different decision tables in the same drd. In the web modeler, some people have only read access to the dmn, so they are not allowed to make any changes. Also, we have the feature to display milestones, basically snapshots of past versions of the file. Those should also not be editable. For those users, I would like to have a read-only view of the dmn modeler, while still having the overview plugin so that they can quickly switch between tables.

Describe the solution you'd like

There are different solutions possible, e.g.:

• Export a viewer in addition to the modeler that can be used like import { CamundaCloudViewer } from 'camunda-dmn-js';
• Expose the overview plugin so it can be used as additional module when instantiating a NavigatedViewer from the core dmn-js library
• Move the overview plugin implementation to the core dmn-js library so it can be more easily used for both Viewers and Modelers

Describe alternatives you've considered

For now we keep the custom implementation of the overview feature in the web modeler that we can integrate with both viewer and modeler.

Additional context

[nikku]

Moved to spring cleaning.