fdctl metadata descriptors (fd_pod) for better object discovery

[ripatel-fd]

Problem

Joining shared memory objects of a production fdctl instance is excessively difficult.

Object discovery currently involves recreating all setup steps (parsing a config file, constructing the topology, and simulating tile initialization code to recover object offsets). It also breaks across different versions.

Suggested Fix

Use fd_pod or similar to place "directories" at known locations of workspaces, so that objects can be easily discovered.