Create a simple way to run all acceptance tests with different authentication schemes.

Current `docker-testacc` simply sets the elastic/password credentials which are then used for essentially all tests. We should create a simple way to run the tests with an API key, bearer token etc (even just `make docker-testacc-api-key` might be the good enough).

I had been editing the Makefile to run the full suite with an API key, but it looks like one of the early tests removes any non-system keys and so later tests fail. We'll want to fix that behaviour as part of this change too.