Change description

Adds a template_file config to override the built-in grafana agent config template.

What problem does this solve?

We have multiple agent configs that differ from the built-in config template. We found it was elegant to provide our own template file, and let PromEx specify any defaults and pass through our new custom config keys.

Example usage

config :my_app, MyApp.PromEx,
  grafana_agent: [
    ...
    config_opts: [
      ...
      template_file: Application.app_dir(:my_app, "priv/templates/grafana_agent_config.eex"),
      custom_field: "custom value" # available as <%= @custom_field %> in the template
    ]
  ]

Additional details and screenshots

Checklist

• I have added unit tests to cover my changes.
• I have added documentation to cover my changes.
• My changes have passed unit tests and have been tested E2E in an example project.