Feature Request: "Transfer" as transaction type in CSV import.

[scubamaggo]

Describe the feature

The user should have the ability to add lines representing a "Transfer" in a CSV import. This requires a rework of the import-flow, as this is currently linked to a specific account.

Why is this feature important?

In #883, transfers were introduced as a transaction type. However, they are not yet available in the CSV import flow. As transfers make up a large percentage of transactions in an account portfolio that contains credit cards and investment accounts, having such an import would greatly reduce the manual work. Furthermore, only being able to partially import the list of all transactions from some external account greatly reduces the value of the import, as it forces the user needs to manually go through the list.

Additional context, screenshots, and relevant links

No response