Fix/washboard events

[connorsmith256]

Feature or Problem

This PR fixes two issues:

• it adds a NATS subscription on wasmbus.evt.{lattice} so the washboard can receive events from other hosts, namely the host started/stopped/heartbeat events
• adds missing process_event handlers for events. Some of these are no-ops, and some needed logic (the host started/stopped events)

Related Issues

Fixes #571
Fixes #598

Release Information

Next (preferably v0.62)

Consumer Impact

The washboard is usable for lattices with multiple hosts in them once again :)

Testing

Manual Verification

Tested manually with two hosts, e.g.:

In one terminal:

WASMCLOUD_CLUSTER_SEED=FOO WASMCLOUD_CLUSTER_ISSUERS=BAR PORT=4000 WASMCLOUD_DASHBOARD_PORT=4000 RELEASE_NODE=first-host make run

In another:

WASMCLOUD_CLUSTER_SEED=FOO WASMCLOUD_CLUSTER_ISSUERS=BAR PORT=4001 WASMCLOUD_DASHBOARD_PORT=4001 RELEASE_NODE=second-host make run

I verified that when the second host starts, the first host's washboard immediately recognizes the second host. The second host's washboard will recognize the first host when it receives a heartbeat from the host. I also verified that stopping one host is correctly processed by the other host's washboard state

[autodidaddict]

I'm assuming the literal value BAR doesn't work for the issuers value? :)