service discovery: add state store functionality

events: add state objects and logic for service registrations.

service discovery: add RPC endpoints and FSM logic

service discovery: add HTTP endpoints and sdk wrapper

jobspec: add service block provider parameter

config: add native service discovery admin boolean parameter.

service discovery: add config boolean parameter and fingerprinting

This commit performs refactoring to pull out common service
registration objects into a new `client/serviceregistration`
package. This new package will form the base point for all
client specific service registration functionality.

The Consul specific implementation is not moved as it also
includes non-service registration implementations; this reduces
the blast radius of the changes as well.

client: refactor common service registration objects from Consul.

The service registration wrapper handles sending requests to
backend providers without the caller needing to know this
information. This will be used within the task and alloc runner
service hooks when performing service registration activities.

client: add service registration wrapper to handle providers.

client: add Nomad service registration implementation.

client: hookup service wrapper for use in clients

When a node fails its heart beating a number of actions are taken
to ensure state is cleaned. Service registrations a loosely tied
to nodes, therefore we should remove these from state when a node
is considered terminally down.

cli: add service commands for list, info, and delete.

The service registration client name was used to provide a
distinction between the service block and the service client. This
however creates new wording to understand and does not match the
CLI, therefore this change fixes that so we have a Services
client.

Consul specific objects within the service file have been moved to
the consul location to create a clearer separation.