Improve documentation of `tags` config from tracers/open_telemetry_collector

https://www.benthos.dev/docs/components/tracers/open_telemetry_collector/

Hello, I would like to suggest improving the docs on this component, you see, the docs states:

A map of tags to add to all tracing spans.

But there are some specific keys that require filling, I had to open the source code to find them here:
https://github.com/benthosdev/benthos/blob/main/internal/impl/otlp/tracer_otlp.go#L126
Which come from the keys from the other files here:
https://github.com/open-telemetry/opentelemetry-go/blob/v1.13.0/semconv/v1.13.0/resource.go#L914
Then I realized I had to set the service.name: X tag.

To get to this nice distributed tracing service names:

So I propose we add either all the specific keys one can add, or link to this repo: https://pkg.go.dev/go.opentelemetry.io/otel@v1.13.0/semconv/v1.13.0 to make it easier to know what are some specific tags one can set to achieve what they want.

For example, change the docs to:

A map of tags to add to all tracing spans. The possible tags to be set can be found here: https://pkg.go.dev/go.opentelemetry.io/otel@v1.13.0/semconv/v1.13.0#pkg-constants

Start with the linked OpenTelemetry collector tracer documentation and compare the tags description with the requested example. Document where supported tag keys, including service.name, can be found; done means the page makes these configuration options discoverable without requiring readers to inspect internal/impl/otlp/tracer_otlp.go.