The default ProxyClass can be set via helm chart or env var, and applies
to all proxies that do not otherwise have an explicit ProxyClass set.
This ensures proxies created by the new ProxyGroup CRD are consistent
with the behaviour of existing proxies
Nearby but unrelated changes:
* Fix up double error logs (controller runtime logs returned errors)
* Fix a couple of variable names
Updates #13406
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>