Add shortcuts to assign dynamic tags to Meters

[jonatan-ivanov]

This feature is a shortcut to create/get certain meters in a simpler way using the builder of that meter but without the need of recreating the builder every time.

This is what dynamic tagging looks like before this change (a bit longer and multiple builder instances will be created):

private final MeterRegistry registry = ...;

void favoriteColor(Color color) {
    Counter.builder("colors")
        .tags(Tags.of("color", color.name()))
        .register(registry)
        .increment();
}

And this is what you can do after (a bit shorter and one builder instance will be created):

private final MeterRegistry registry = ...;
private final MeterProvider<Counter> meterProvider = Counter.builder("colors").withRegistry(registry);

void favoriteColor(Color color) {
    meterProvider.withTags(Tags.of("color", color.name())).increment();
}

Closes gh-535
See gh-4092

[jonatan-ivanov]

/cc: @gavlyukovskiy

[gavlyukovskiy]

This looks absolutely awesome!

[jonatan-ivanov]

@gavlyukovskiy @qweek I modified this a little bit, what do you think?

[steven-sheehy]

Why withTags() versus the more commonly used elsewhere tags()?

[shakuzen]

I don't want to speak for @jonatan-ivanov, but I think the idea was to differentiate from the tags() method on the builders because those return a builder and can chain, whereas this method returns a registered Meter and cannot be chained to add more tags. I spent some time trying to think of better naming, but I was not able to come up with something. This is definitely something we're hoping to get feedback on and improve. Ideally, we would not change the naming after RC1, but it may be worth making an exception in this case if we cannot come up with something better before merging this.

[jonatan-ivanov]

Yeah, tags might be confusing since that is on the Builder as well as MeterProvider.