Full support for code workflows inside the UI with v3

Currently it is possible to set the `Published` flag in the SqliteDb (maybe also possible with C# code but not tried yet) but it is not possible to do this inside the Web UI.
Inside the Web UI code workflows will not be shown within the "Workflow Definitions" page and therefore there is no possibility to unpublish/republish code workflows.

What I would like to have:

1. Call `elsa.AddWorkflow();` with some kind of parameter to set the initial published state. Our usecase is to create code workflows which should be unpublished by default and if the user will enable such a workflow they have to publish it manually.
2. Show code workflows inside the "Workflow Definitions" page with the limitation that it can't be edited but publish/unpublish should be possible and it should be possible to see all activities with its settings
3. Show executed code workflow instances within the "Workflow Instances" page. This is already possible but if you click on such an instance you don't see much infos

Start by tracing the Elsa.AddWorkflow() registration and the existing SqliteDb Published flag behavior. Then inspect the Web UI's Workflow Definitions and Workflow Instances pages, using the listed requirements as the completion criteria: configurable initial publication, publish/unpublish and activity settings for code workflows, and useful details for executed code workflow instances.

Written by the indexing model from the issue text.