Add code locations to Metrics

[AbhiPrasad]

Problem Statement

Metrics allows supports adding code locations via a separate metric_meta envelope: https://develop.sentry.dev/sdk/metrics/#meta-data

We should add support for this!

Solution Brainstorm

### Todo
- [ ] Add `metric_meta` envelope
- [ ] Add support for code locations to browser metrics aggregator
- [ ] Add support for code locations to server metrics aggregator
- [ ] Validate that code locations works sourcemaps

[AbhiPrasad]

This is a won't do with the recent changes to metrics.

[jeengbe]

@AbhiPrasad could you share a link to the changes you mentioned, please? 🙂 Is it this?

[AbhiPrasad]

Is it this?

Yup - the shift to having metrics always be connected to spans means that you can often identify execution context just with spans, so there is less need for code locations.

In addition for JavaScript there is the added complexity of sourcemapping, which means that code locations would need extra setup for sentry and the user.