Ability to use a custom apm-server.yml file to start APM Server using Tilt

Currently while running Tilt, the `apm-server.yml` file is referred from inside the docker container and there's no way to override APM Server settings. As a user one should be able to provide a custom `apm-server.yml` file (or the one present at project root) which could be volume mounted or somehow referenced while running the docker container.

Suggestion from @marclop is to invest time in a Helm Chart to achieve the same.

Start by inspecting the Tilt configuration and the current Docker reference to apm-server.yml. Compare the proposed Helm Chart approach with volume-mounting a project-root apm-server.yml, and consider the work done when a custom settings file can be supplied while starting APM Server with Tilt.

Written by the indexing model from the issue text.