Our resource implementation does not currently consider the (optional) concept of Schema URLs (as described in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/resource/sdk.md#resource-creation).

To support this, we'll have to add it to the create and merge operations on the Resource, and we'll have to adapt the @opentelemetry/otlp-transformer package so that it populates the schema URL with the one from the SDK's resource

This issue is considered done when:

• Schema URL can be added using the Resource constructor
• Schema URL is handled according to the specification on Resource#merge
• A resource's Schema URL is exported via all OTLP exporters in this repository.