Remove common models from NRF

Changes

• Remove all common models which are in common-src (see oai-cn5g-common-src!23 (merged))
• Change namespace from oai::nrf::model to oai::model::nrf
• Change namespace in models when pointing to common models
• Remove some dangerous (⚠) using namespace statements in header files

Feature

• While we do not implement it in the service layer, the changes I did in DiscNFInstancesStoreApi.h/cpp allow to generate models from query string parameters. That was previously not implemented.

Note to review

@tien-thinh.nguyen Like with all this MRs, most changes are trivial and are just namespace changes and moving some stuff.