Add otellog test recorder

[Kloh-Dev]

Based on unit tests, that verify if certain messages were logged e.g. in specific levels, we need a simple mechanism to give such a opportunity.

This PR contains everything to be able to use e.g. this snippet in your tests:

import (
    "github.com/d-velop/dvelop-sdk-go/otellog/otellogtest"
    "testing"
)

func TestXXX(t *testing.T) {
	logRecorder := otellogtest.NewLogRecorder(t)
	
	// do your tests

	logRecorder.ShouldHaveLogged("expected-log-message", otellog.SeverityXXX)
}