This includes code that can still read the old V1 format, and convert
it to the new ComputeSpecV2 struct.
For better test coverage of the upgrade function, update the sample V1
cluster spec file in the tests to match more closely what the control
plane actually generates.
The intention is to change the real web console to also use the V2 format,
and then remove the support for V1 format altogether.
This is in preparation of using compute_ctl to launch postgres nodes
in the neon_local control plane. And seems like a good idea to
separate the public interfaces anyway.
One non-mechanical change here is that the 'metrics' field is moved
under the Mutex, instead of using atomics. We were not using atomics
for performance but for convenience here, and it seems more clear to
not use atomics in the model for the HTTP response type.
