Add extra resource attributes to config

[oxcafedead]

Currently, there is no API to insert custom resource attributes.
For example, to set deployment.environment semantic attribute from OpenTelemetry Semantic Conventions, one has to do smth like:

		postProcessor: (spans) => {
			if (spans.length == 0) {
				return spans;
			}
			const resource = spans[0].resource;
			resource.attributes['deployment.environment'] = env.ENV_NAME;
			return spans;
		}

Ideally, would go great to have it configurable

As I am not sure about proper naming / place to put this -- feel free to throw it away or change, but the overall idea is:

	return {
		exporter: {
			url: tracesEndpoint,
		},
		service: {
			name: serviceName,
			version: env.VERSION,
		},
                extraResourceAttributes: parseAttributes(env.OTEL_ATTRS)),
...

Also not sure if we should update readme as this is not an essential config part.