Runner Role Assignment

## Overview

Add command for setting roles: https://www.elastic.co/guide/en/cloud-enterprise/2.9/set-runner-roles.html

## Possible Implementation

## Testing

## Context

Part of the workflow of replacing directors is to demote the runner but before you do that you must unassign the role. The current API supports managing runner roles but ecctl doesn't have support for the operation yet.

## Your Environment