build: client_library flag to build only used modules, remove package yaml (#1394)

* move dependencies to library

* remove package.yaml

* remove auto-generated comment

* cleanup target definitions

* add executable options

* add test rtsopts

* revert common options

* don't hide unused packages warning

* Add client_only cabal flag (#1396)

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Co-authored-by: IC Rainbow <[email protected]>
Co-authored-by: Alexander Bondarenko <[email protected]>

Author: epoberezkin