[exporter-metrics-otlp-proto] Add browser support

[pichlermarc]

Is your feature request related to a problem? Please describe.

Currently both @opentelemetry/exporter-trace-otlp-proto and @opentelemetry/exporter-logs-otlp-proto offer browser support, but @opentelemetry/exporter-metrics-otlp-proto does not. We should also add support for it to @opentelemetry/exporter-metrics-otlp-proto.

Describe the solution you'd like

Add browser support to @opentelemetry/exporter-metrics-otlp-proto. #4097 is a prerequisite for that.

Additional context

• discovered that this feature is missing while investigating ESM build of exporter-metrics-otlp-proto@0.41.1 fails when target=denonext #4044

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[pichlermarc]

I'm actually working on this as part of a major exporter overhaul that will make exporter easier to work on and test.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[pichlermarc]

Not stale. A draft for this is included in #4415