Add support for OpenTelemetry resource attributes

[brettmc]

What is the underlying problem you're trying to solve?

I would like the traces emitted by OPA to contain custom resource attributes that I provide. For example, service.namespace, which allows me to differentiate between the traces from multiple OPA instances.

Describe the ideal solution

Provide distributed_tracing.resource_attributes config, which accepts a list of key-value pairs, which are passed along to the OpenTelemetry SDK. Most OpenTelemetry SDKs do this via the OTEL_RESOURCE_ATTRIBUTES environment variable, and those would be passed to the tracer provider

Describe a "Good Enough" solution

Using https://opentelemetry.io/docs/languages/go/resources/ resource.WithFromEnv()in

opa/internal/distributedtracing/distributedtracing.go

Line 102 in 291825e

res, err := resource.New(ctx,

could allow providing resource attributes from the environment

Additional Context

[ashutosh-narkar]

This seems like a good addition. Updating the config to provide key-value pairs seems like a good approach. Feel free to contribute this feature if you'd like.