Tracing

[vascoguita]

No description provided.

[labkode]

@gmgigi96 @glpatcern this may look it's a big PR with many crucial changes but is not. Most changes are just adding the instrumentation to the code, modulo there is some refactoring of the tracing logic.

I would like to test this PR in the QA environment to start getting some load to find perf limits, however I prefer to follow the typical release cycle to merge this and generate a new version that will be deployed only on QA.

I went with Vasco through the code and looks good, the configuration is already in Puppet.

Please do a review as well and then we can tag.

[glpatcern]

I think it's fine to go ahead for QA field tests. My only comment would be on the style of coding the SpanStart calls spread over the whole code base, which all look like:

r, span := tracing.SpanStartFromRequest(r, tracerName, "<name of the function>")

or

ctx, span := tracing.SpanStartFromContext(ctx, tracerName, "<name of the function>")

where the name of the function is hard coded each time. If some reflection logic could be used, that could be worked out from the calling stack instead, but I'm not sure this is at all possible in Go.