Add support for sending additional HTTP or gRPC headers which
can be used for authentication or other additional information
for the tracing system without having to set up a local instance
of the OpenTelemetry Collector to add these headers.
Example with Dash0:
```yaml
tracing-enabled: false
tracing-transport: "grpc"
tracing-endpoint: "ingress.eu-west-1.aws.dash0.com:4317"
tracing-headers:
"Authorization": "Bearer DASH0_AUTH_TOKEN"
"Dash0-Dataset": "gotosocial"
```
Example with Honeycomb:
```yaml
tracing-enabled: false
tracing-transport: "grpc"
tracing-endpoint: "api.honeycomb.io:443"
tracing-headers:
"x-honeycomb-team": "YOUR_API_KEY"
"x-honeycomb-dataset": "YOUR_DATASET"
```
Neither Semaphore nor Pinafore are under active development, but
Semaphore has archived its repository while Pinafore still gets
occasional minor maintenance.
Enafore has newer features, but it has accessibility bugs affecting
screen readers that prevent it from being recommended at this time.
