Add NGINX receiver

[awiddersheim]

Is your feature request related to a problem? Please describe.

We would like to use ADOT to gather metrics from NGINX. There is already a receiver for this that just scrapes the NGINX status endpoint.

Describe the solution you'd like
The NGINX receiver added to ADOT.

Describe alternatives you've considered
There are some alternatives out there like exposing the NGINX metrics as a Prometheus endpoint (similar to an HAProxy feature) but it requires running yet another sidecar which seems excessive giving the availability of the upstream receiver.

Additional context
Nope.

[Aneurysm9]

We do not currently plan to include this receiver in the ADOT Collector distribution. At this time we recommend using a system that can expose the NGINX metrics as Prometheus exposition and using the prometheus receiver. We will leave this issue open to track interest in including this receiver in the ADOT Collector distribution.