Change the directory structure used for starter pipeline tests to match the new structure used on `kedro pipeline create`

[lrcouto]

Description

With the changes to the directory structure applied in https://github.com/kedro-org/kedro/pull/3731 now merged, @ankatiyar proposed updating the structure of folders created by the Kedro starters to match them.

Context

The current structure has the pipeline tests created by starters placed in <project root>/tests/pipelines, while the tests created from the kedro pipeline create command go into <project root>/tests/pipelines/<pipeline name>. What is being proposed is to put the pipeline tests from starters into their own directory as well.

For example:

In the image above, we can see test_data_science.py that was created by using the spaceflights-pandas starter and is located directly in the tests directory. The test file for my_pipeline, which was created with kedro pipeline create, is on it's own directory.

Possible Implementation

The initial idea would be putting the pipeline tests generated from starters on their own directory. In the aforementioned example, the structure would change from <project root>/tests/pipelines/test_data_science.py to <project root>/tests/pipelines/data_science/test_pipeline.py.

[astrojuanlu]

Would it make sense to try to fit this for the upcoming 0.19.4 to avoid inconsistencies @merelcht ?

[merelcht]

Would it make sense to try to fit this for the upcoming 0.19.4 to avoid inconsistencies @merelcht ?

Yes this must be done before the release.