take out metadata to start with and make opaque later

[weissi]

On the forums , a few have rightly pointed out that currently, there's two places to get/set the metadata:

logger[metdataKey: "foo"] = "bar"

and

logger.metadata["foo"] = "bar"

The intention is to always use the former (logger[metdataKey: "foo"] = "bar") unless you want to store/retrieve the whole metadata storage, for example for MDC.

But as it was correctly pointed out, if that's the case we could/should make it opaque.

My proposal for right now is that the LogHandlers need to support both but the Logger should only expose the subscript. In a new minor version that we can release anytime, we could then add a back a well-designed story for MDC and friends.

[weissi]

CC @tomerd

[ktoso]

Sounds good to rip our now and design on later.

For tracking the progress though, I think this ticket will be closed as the "rip out" part, so I'll open up the "design it" adding one of the use-cases, sounds good?