Extract prometheus metrics #1

[kuritka]

Related to #255
This is the first part of larger refactoring.

• move Dig to utils
• move prettyPrint() to utils and rename to ToJSON()
• cover ToJSON() by tests
• move environment variable POD_NAMESPACE to depresolver
• extend depresolver tests
• extend depresolver validators for namespace validator
• extract Prometheus metrics into standalone module
• extend Prometheus metrics with Register(),Unregister()
• remove controllers/metrics.go
• fix controller tests
• remove dead registry/k3s.yaml file (pushed by mistake)

TODO:

• dnsupdate refactor, to provider pattern, will come in the next PR
• finally, some utils will go into gopkg
• IMetrics introduction (should be implemented with Expose advanced metrics #124)

[ytsarev]

Look good, but not sure if ToJSON is properly reflecting semantics... Originally the function was created just for readable struct printing...

[somaritane]

I'd probably separate Dig and prettyPrint refactoring to different PRs, as they are out of context of this PR

[kuritka]

Look good, but not sure if ToJSON is properly reflecting semantics... Originally the function was created just for readable struct printing...

I see, but function accepts interface so can be used to any type. Of course I can limit to structures only, and return error if passed argument is not structure.
Do you think rename may help ? What about ToString(a interface{}) string ?

str{"Foo", 007} => 

{
	"Name": "Foo",
	"Value": 7
}

123 => "123"
true => "true"
nil => "null"  // marshalling implicitly returns this, but can be changed. 

[kuritka]

I'd probably separate Dig and prettyPrint refactoring to different PRs, as they are out of context of this PR

@somaritane, amended.

[somaritane]

lgtm 👍

[ytsarev]

looks good