Add newrelic as an output option

[simskij]

Currently, only the datadog collector supporting sending tags. However, other popular implementations support sending and receiving tags as well:

• https://github.com/atlassian/gostatsd
• https://github.com/newrelic/nri-statsd.

Feature Description

I want to be able to send statsd metrics with tags to nri-statsd without having to use --out datadog as the result output. Running k6 with the --out datadog, but pointing it at nri-statsd works, although looking awkward and not being that intuitive.

Suggested Solution (optional)

• Create another alias so that --out datadog and --out newrelic may both be used for the existing implementation
• Add --out newrelic as a separate option
• Add a parameter that enables the sending of tags in --out statsd

[na--]

I'd prefer the last suggested option. I don't know the details of the data format and its various implementations, but maybe something like a version option to the current statsd collector, with v1 being the default current implementation and v2 being usable for datadog, newrelic and any other similar services.

Alternatively, if statsd v2 is not really a standard, or if there are some differences between the proprietary implementations of NewRelic and DataDog, maybe we can have a variant option instead, with the possible values of original, newrelic, and datadog? 🤷‍♂️

Outputs are currently fairly painful to add in k6 and we hope to fix that (and enable output xk6 extensions) in k6 v0.31.0, so ~March. That should unlock a lot of flexibility and it might make sense to add separate outputs then. Though, to me, it's more likely that we'd like to merge the current datadog output, which already shares most of its code with the statsd one, e.g. make it an alias to statsd{version=v2} or whatever.

That said, I am not familiar with the ecosystem, so I may be very wrong. For example, if some proprietary statsd-based service has some significant feature not available in others, it might make sense to have a separate output for it... 🤷‍♂️