Redpanda Self Test / Test Orchestration and Management - Part one

[graphcareful]

Cover letter

This is the first of a series of commits that make up the new self test feature, RFC

This patch set contains the infrastructure and tooling necessary to start, stop and retrieve results from self tests. Clients control the behavior via the admin API. All brokers include a new self test RPC service used to communicate with each other. The leader node is responsible for test orchestration among all peers.

Release notes

• none