update nginx related quickstarters to support autodiscovery of services for APM solutions

[gerardcl]

Is your feature request related to a problem? Please describe.
When using a quickstarter that runs nginx most of the APM solutions out there that implement autodiscovery define the service discovered name as "_" or "localhost". It should have a better meaningful name like "gateway" or "nginx" or the name of the quickstarter like "nginx-ionic" or "gateway-ionic".

Describe the solution you'd like
Set the nginx.conf attribute "service_name" to something meaningful instead of "_".

Describe alternatives you've considered
I would like to gather some suggestions to not only be me deciding on what names should be the default.

Additional context
So far, this happens in:

• be-gateway-nginx
• fe-ionic
• fe-angular