add support for datadog-installer

[chouquette]

This PR adds initial support for the datadog-installer. It will install it if APM is enabled, as is the case for the install script, and will delegate installation of the injector and tracer libraries to it. Installation of tracer libraries are now gated behind a check that ensures the installer doesn't currently own that package. It also provides telemetry similar to what the install script provides BARX-381

[raphaelgavache]

I'm not familiar enough with Ansible and I couldn't from the PR reading assert this:

APM install scripts need to be gated on apm-inject installation by the injector

If the injector is installing apm-inject the scripts shouldn't run.

[chouquette]

I'm not familiar enough with Ansible and I couldn't from the PR reading assert this:

APM install scripts need to be gated on apm-inject installation by the injector

If the injector is installing apm-inject the scripts shouldn't run.

Thanks for spotting! This should now be fixed I think the entirety of apm-inject-install.yml should be disabled as it also includes some package pinning and listing what's installed by apt/rpm, but we might want to introduce something similar to list what the installer installed.

[chouquette]

I think the entirety of apm-inject-install.yml should be disabled

The CI begs to differ :sweat_smile:

[chouquette]

It works better when installing the tracers that are not handled by the installer, who'd have thought :facepalm: