This change removes the hard-link from templates to worker pools,
allowing pools to be selected using k8s labels.
Both actors and actor templates are augmented with a label selector
field.
When an actor is resumed, we resolve the set of *eligible* worker pools
by evaluating the intersection of both actor and template selectors.
Then we find a free worker from one of them. The overall design is
described in [1].
[1]:
https://github.com/agent-substrate/substrate/issues/47#issuecomment-4712334620
Implements `PAUSED` state for issue #119.
The snapshot files are kept locally on node VM in a separate folder. At
resume time, scheduler uses a node VM hint and picks up a worker from
the same node where files were stored at suspend time.
The local file management solution is temporary and will be replaced
once @msau42 introduces a new component that is supposed to manage files
on the node VM.
- [X] Tests pass
- [X] Manual tests with counter demo
```
>kubectl ate create actor my-counter-1 --template ate-demo-counter/counter
>curl -X POST -H "Host: my-counter-1.actors.resources.substrate.ate.dev" http://localhost:8000
hello from: 169.254.17.2 | preserved memory count: 1
>curl -X POST -H "Host: my-counter-1.actors.resources.substrate.ate.dev" http://localhost:8000
hello from: 169.254.17.2 | preserved memory count: 2
>kubectl ate pause actor my-counter-1 -o json
> curl -X POST -H "Host: my-counter-1.actors.resources.substrate.ate.dev" http://localhost:8000
hello from: 169.254.17.2 | preserved memory count: 3
```
### Breaking change
This PR introduces a breaking change in the Actor proto. All existing
actor needs to be recreated, prior testing PAUSE functionality.
Julian Gutierrez Oschmann