[QoL / UX improvement] Add advanced data selection

h1. Issue

Currently the migration from e.g. customer and orders has a bunch of dependencies, which has to be fetched before you fetch the main entity (the customer or the order). For the first migration run its necessary e.g. to migrate the customer to migrate the orders, but in all other runs after you maybe don’t want to migrate them again and again.

h1. Proposal

Creating a new tab “advanced data selection“ in the migration main page. On this page you can select the data sets instead of the data selections, in fact of this you can chose what to migrate in detail e.g. you can only select the customer.

h1. UI / UX proposal

Something like the detailed permissions list would be a good in my pov. We have to check what is possible on technical side and what we have to change for this, but advanced users should have the possibility to chose individual data sets instead of whole data selections and the migration process will order them correctly.

h1. Technical proposal

We have to watch out, how we could implement this in JS, because currently we only use the data selections and we also have to take care about the “supports“ function of the premapping, these only looking for the data selections instead of the data sets.

h1. Additionally

We should also add the possibility to the CLI, that the user also could select the datasets there.

Start by tracing the migration main page, its data selections and data sets, the premapping supports function, and the CLI selection flow. Determine how individual datasets can be selected while preserving migration ordering, then verify equivalent behavior in the UI and CLI.

Written by the indexing model from the issue text.