feat: add template for elastic apm traces

[gvencadze]

Adds support for Elastic APM traces.

(didn't include tests)

[hexdigest]

Hi @gvencadze , please take a look at this template: https://github.com/hexdigest/gowrap/blob/master/templates/elasticapm

maybe it's what you need.

[gvencadze]

@hexdigest o_O, I've created this merge request 3 week earlier.

Btw, there's a bug while call _d.captureError() - we must call Send() method to send error to APM system, otherwise it won't be sent.

Also span type is incorrect - they should have names like "http", "db", "external", "internal" and not interface name, I'll suggest this changes in another MR, okay?

[bars43ru]

Consider the opportunity by the naming of the span, using opt function pattern, which in turn allows you to either use the base type or set the name manually

[bars43ru]

@gvencadze, thanks for the note about the Send() call, I'll fix it now.

[gvencadze]

@bars43ru

I'll suggest to avoid setting each parameter from function to labels, better add them via opt function

[bars43ru]

@gvencadze It looks like really use/not use 'SetLable' can be controlled through opt function. This will allow for a more general pattern.

[bars43ru]

a little later I will prepare an MR with the ability to manage the use SetLabel via opt function

[gvencadze]

@bars43ru you can tag me in MR - I've some experience with elastic apm, maybe I'll suggest anything else to make template better