[services][blob] Move current implementation to cpp directory
Summary:
Until the Rust implementation is complete, the current C++ implementation
can live next to it.
- Moved the C++ Blob Service code to the services/blob/cpp directory
- Adjusted Dockerfile and CMakeLists.txt to use the new location
Test Plan:
Docker image builds, the following commands are executing successfully:
- yarn run-blob-service
- yarn run-integration-tests blob
Reviewers: varun, jon, tomek, marcin
Reviewed By: tomek
Subscribers: ashoat, atul
Differential Revision: https://phab.comm.dev/D5675