Support batch-size limits for OTLP payloads from Lightstep metrics SDK

[jmacd]

Is your feature request related to a problem? Please describe.
Because a single interval computes a single protocol message, there is no current feature allowing users to place limits on metrics size. Generally, this means when you overuse metrics you eventually reach a gRPC max-message-size limit.

Describe the solution you'd like
Batching by size is not an easy problem. I've seen https://pkg.go.dev/google.golang.org/api/support/bundler is one approach. (I developed something similar for Lightstep satellites.)

Simpler to batch by maximum point count and leave it to the user's attribute/resource size to determine max payload.

Describe alternatives you've considered
This is difficult to specify at the OTel level. The alternative is not to do this.

[jmacd]

The batchprocessor is now supported, which splits large payloads.