Create system state entry in dataman - ATTN Anton

Create persistent system state id for data manager to store system state
that will persist across resets.
No it is not required if you are only reading the data. Locking is only required to avoid race conditions where two independent processes might read, modify, and write back the data. Consider the following scenario:

process a reads the state.
process b reads the state.
process a modifies the state.
process b modifies the state
process a writes the state
process b writes the state.

Changes made by process a are lost!

This is not strictly necessary now since only mavlink will read-modify-write the state. But is we want to generalise the system state to contain other independent data, locking will be required for any thread that reads, modifies, then writes the system state.