Create `nv_ingest_common` Python module

Create an empty, or as empty as possible, nv_ingest_common Python module in the nv-ingest codebase. This should include the necessary files to build nv_ingest_common via Pip with a pyproject.toml file declaring and housing the build metadata.

Furthermore both nv_ingest and nv_ingest_client modules should be adjusted and validated that they can include the empty nv_ingest_common module as one of their dependencies.

All existing build and Dockerfiles should also be adjusted to ensure that existing build pipelines do not fail and account for the new building and packaging of the nv_ingest_common module.