Add tracing capability for Webhook

[thisthat]

Goal

Instrument the Webhook with the OTel SDK to export traces.

Technical Details

Use OTel Go to manually instrument the code to export the following spans as a single trace:

The Trace Context should be propagated into the CRDs via a common metadata field TraceContext. The context will be propagated using these immutable fields. This struct should look like the following:

type KeptnContext struct {
	TraceID    string `json:"traceparent",omitempty`
	TraceState string `json:"tracestate",omitempty`
}

The webhook shall use keptn/webhook as the component name.
Spans shall be created with the following OTel Attribute:

• KeptnApp
• KeptnWorkload
• KeptnInstance
• KeptnVersion

The webhook is the one that always starts a trace.

Acceptance Criteria

• TraceContext contains W3C Trace Headers
• Webhook creates a Server Span when it starts to handle a request
• Webhook creates a Producer Span when it creates the Workload CRD
• Webhook injects the W3C Context into the CRDs
• Attributes with Keptn information are added to the Span

DoD

• The Webhook exports traces

Resources

• https://github.com/open-telemetry/opentelemetry-go/tree/main/example