feat: Improved metrics setup

[nhhagen]

Closes: #433

[hawi74]

I think we shouldn't allow clients of this lib to remove the default tags (environment:*, service:* and version:*), especially since the lib cannot be initiailized if env vars for those tags are missing. Maybe change the func name to WithExtraTags() and append passed tags to options.tags instead of replacing them?

func WithExtraTags(tags ...string) Option {
	return func(options *options) error {
		options.tags = append(options.tags, tags...)
		return nil
	}
}

[nhhagen]

I agree the default ones should not be removed. I prefer the name WithTags. I'll ensure the default ones are not removed when setting tags. I want having to support repetitive calls to the function as well.