add load balancer basic features to README
Update default healthcheck URI to be '/'

A healthcheck URI of '' (which technically is the defualt if no
Uri is provided) results in a healthcheck request of 'OPTIONS *'.

This is rejected with a 400 by Nginx and likely other servers, and
so is not really a sensible default - vCloud Director considers the 400
a bad request, and marks the member node as down.

Instead, use '/' as the default healthcheck Uri, as this then maps
to a 'GET /' call, generally returning ok by most sites.

NB: This vCloud Director documentation suggests that the default is /
    regardless. This at least makes our tool match the docs.
Bump version and update CHANGELOG
Merge branch 'master' into load_balancer_readme
add pool service details to README
add basic virtual_server details to README
reword CHANGELOG message for clarity
add load balancer persistence details
improve usage-notes for load balancer
load balancer README updates from feedback
Refactor out the 'test_cases' array

The test_cases array is not useful in the generators tests,
and has caused problems.

This refactors it into individual test cases, as per NatService
generator.
Clarify CHANGELOG

It didn't make it clear which URI caused 'OPTIONS *'.

Also updating previous bugfix message - it's not broken, it's now fixed.
Merge pull request #21 from alphagov/66941992_uri_fix

[#66941992] Update heathcheck URI to fetch '/'.
Merge pull request #26 from alphagov/66785404_firewall_tests

[#66785404] Refactor out the 'test_cases' array from Firewall generator tests
Merge pull request #24 from alphagov/load_balancer_readme

[#65881616] Load balancer documentation
Use validator in Core
Remove local config validator
Use Core's Config Loader
Remove local config loader
This isn't an integration test

It also fails, because the Core logger now receives the error, not the EdgeGateway logger. However, this is not a great way to test it. This will be dealt with by fixing a combination of the issues raised in the story - injecting the loaded config and testing the schemas.