[Bug]: Decide where to keep `picks`code

[gogonzo]

See related discussion https://github.com/insightsengineering/coredev-tasks/discussions/684

What happened?

New package or in teal.transform or in teal. On the diagram below relationship between elements are depicted.
New tools are mostly independent except wrappers/converters (as.picks, teal_transform_filter).

Arrows represent what is used where

[gogonzo]

Decision to continue support of teal.transform should be conditional upon #281

Please also consider that des <-> picks is not possible, which means that shiny modules in the package will have to be maintained separately.