[services] Tunnelbroker - Add copying of the shared directory to the Dockerfile

Summary:
This diff introduces changes to the Dockerfile to copy the /shared directory to the service Docker container.
In a ENG-1698 we have introduced a new directory for the shared objects.

To make the Tunnelbroker built in D4807 and beyond updates, we need to copy the /shared folder to the Docker container.

Related Linear tasks: ENG-1698, ENG-1672

Test Plan: Successfully built in a D4807 using the cmake/corrosion-cxx.cmake file from the shared directory.

Reviewers: karol, tomek, jon

Reviewed By: karol, tomek

Subscribers: ashoat, tomek, atul, karol, abosh

Differential Revision: https://phab.comm.dev/D4949