Instantiate subnet stack when restarting peer

[adlrocha]

If an Eudico peer has joined a subnet, it should be able to instantiate and re-sync with the subnet after restarting the client. This is not the case in the current implementation. We'll fix this by:

• Persisting state about the subnets a node is syncing with.
• Automatically sync with all the subnets a node was syncing before restarting.
• Additionally, we should include a cmd for nodes to be able to check the list of subnets they are currently syncing with.

We can approach this in different ways:

• When the eudico process is started and the subnet manager is instantiated, we check that state of the different subnets actors and automatically start a new subnet process to sync with the ones we are part.
• We add a sync command for subnets that can be used to explicitly sync with a subnet that we are part of. This prevents from automatically joining every subnet we are a member of when restarting our node.
• We use a config file to specify the subnets to sync with when we start our node (this approach is quite static, it may be useful to support it, but more dynamic approaches as the aforementioned should also be considered).

[adlrocha]

As discussed sync with the team, clients should automatically sync with every subnet they are part of. This may require persisting the subnets we are participating on to prevent from having to loop through all subnets to see if we are part of them.

editing in issue description