Add support for user defined OTEL resource attributes

[clly]

This will add support for pulling in opentelemetry's default attributes
It adds sdk information, service.name and discrete key/value entries as
specified on the environment and local host information such as the
hostname and instance.

[bboreham]

Thanks for the PR.

Can you describe how those attributes are useful for Kspan? It generates spans that claim to come from many different components such as kubectl, scheduler, controller-manager, so I wonder if it would be confusing that they all have the same host information.

[clly]

Sorry about that. One of the default attributes is also anything that exists in the OTEL_RESOURCE_ATTRIBUTES environment variable.

This change pulls that in as well as all the SDK and local host/runtime environment information

[clly]

It is possible to only pull in the environment variable attributes instead of everything. If that's preferred let me know and I can change it

[bboreham]

Yes, might be safer to start just with the env-vars.

[clly]

I've updated the PR to only pull in resources from the environment