Decouple starters from framework in tool selection flow

[merelcht]

Description

With the addition of the tools flow some coupling between framework and the starters was added in the post_gen_project scripts: see https://github.com/kedro-org/kedro-starters/blob/main/spaceflights-pyspark/hooks/post_gen_project.py

Unit tests for the tools selection have become hard to maintain see e.g. #3594, because framework needs to pull the starters. If we can somehow decouple the tools selection process better the tests might become simpler too.

Context

See #3594 (comment)

Possible Implementation

The checks here: https://github.com/kedro-org/kedro-starters/blob/main/spaceflights-pyspark/hooks/post_gen_project.py#L30 shouldn't be needed because at this point the tool selection should already have been checked and verified on the Kedro side. This might mean we can move the main function to Kedro.