NewRegistry takes a map of `plugintype` to PluginDispenser functions that should be used to vend clients for plugins to be used.

EventTypeDeregistered is emitted by the Registry when a plugin has been removed.

EventTypeRegistered is emitted by the Registry when a new plugin has been registered.

PluginConnectionInfo is the data required to connect to the plugin.

PluginInfo is the metadata that is stored by the registry for a given plugin.

PluginUpdateEvent is a struct that is sent over a PluginsUpdatedCh when plugins are added or removed from the registry.

RegistryState is what we persist in the client state store.

Registry is an interface that allows for the dynamic registration of plugins that are running as Nomad Tasks.

StateStorage is used to persist the dynamic plugin registry's state across agent restarts.

EventType is the enum of events that will be emitted by a Registry's PluginsUpdatedCh.