[Python O11Y] Fix core header dependency issue

[XuanWang-Amos]

Core team moved resolver code to src/core/resolver, our build is failing because we have a dependency on it and the resolver folder is not copied to observability/grpc_root:

• call_tracer.h -> core_configuration.h -> lb_policy_registry.h -> lb_policy.h -> endpoint_addresses.h

To fix this issue and to prevent such issues from happening again, instead of subfolders, we'll copy all files from src/core to observability/grpc_root/src/core.

Artifact Size:

• Before this change, ~4.7MB: (grpcio_observability-1.62.0.dev0-cp312-cp312-linux_x86_64.whl)
• After this change, ~4.7MB: (grpcio_observability-1.62.0.dev0-cp312-cp312-linux_x86_64.whl)

[gnossen]

How do we get this dependency? Can you give me the pathway in terms of C++ files?

[XuanWang-Amos]

How do we get this dependency? Can you give me the pathway in terms of C++ files?

It's in the description.