Generate runtime metrics

[pablochacin]

Description

Add options to the agent for generating go runtime metrics.

Fixes: #199

Checklist:

• My code follows the coding style of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• Any dependent changes have been merged and published in downstream modules
  

[roobre]

Left some comments. I wonder thought how this will evolve when we transition to daemon mode, as I think Prometheus might make more sense in that case. IIRC the prometheus go library can collect this metrics for us.

[roobre]

collector seems a bit strange as a name for a cancel function, what about cancelCollector?

[pablochacin]

Makes sense

[roobre]

I'm not seeing how this goroutine exits when the context is cancelled. Wouldn't the goroutine be looping forever when ctx.Done() returns a closed channel?

A maybe simpler approach could be to:

Suggested change

	go func() {
	ticks := time.NewTicker(m.rate)
	for {
	select {
	case <-ticks.C:
	m.sample()
	case <-ctx.Done():
	ticks.Stop()
	m.generate()
	}
	}
	}()
	go func() {
	ticks := time.NewTicker(m.rate)
	defer ticks.Stop()
	for {
	select {
	case <-ticks.C:
	m.sample()
	case <-ctx.Done():
	m.generate()
	return
	}
	}
	}()

[pablochacin]

Good catch. Thanks

[roobre]

Looking good!