Add support for configuring APM injection

[rarguelloF]

This PR adds support for configuring APM injection for a host (see: https://docs.datadoghq.com/tracing/trace_collection/library_injection_local/?tab=host#configure-docker-injection).

The supported scenarios are:

• Agent and applications running on the same host (datadog_apm_instrumentation_enabled: host).
• Agent and applications running in separate Docker containers on the same host (datadog_apm_instrumentation_enabled: docker).
• All the previous scenarios at the same time (datadog_apm_instrumentation_enabled: all).

[bkabrda]

Hi 👋 thanks for sending a PR. I think this is a good start, but it will need some more work. I left comments inline addressing what needs to be done.

[bkabrda]

Hi 👋 thanks for the additional work, this looks much better now! I left couple comments to address inline. I would also like to ask you to add the descriptions of all newly added configuration values to the README.md file.

[hestonhoffman]

Small edit

[bkabrda]

Hi 👋 this now looks almost ready, but I still found some problems that should be addressed before I can approve.

[bkabrda]

LGTM now, great job!

[maxiangelo]

Hi didnt you forgot the Agent on host, app in containers possibillity of injecting APM?