[angular] Prepare folders in entity-client subgenerator for tests next to files they are testing

[kaidohallik]

This is the second PR according to #13125 (comment)

entity-management has already now too much files in one folder but after adding tests there, it's really badly readable, so splitting different components into different subfolders: list, detail, update, delete

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[pascalgrimaud]

same here I'm trusting you, @kaidohallik so go ahead and merge it, if you feel confident :)

[kaidohallik]

OK, @pascalgrimaud, I'm marking this PR as draft for now to think about how to proceed after #13125 (comment)

[kaidohallik]

I'm merging this. If moving tests away from test folder then anyway whole spec folder will be deleted so no problem here.