feature: support of link button for the observability backend (for task instances)

In the DAG run page, it may be great to have a button that, when someone clicks, could open up the web page of the observability backend that shows the trace itself.

Since there can be many varients of the backend, defining the link could be done via environment variable that can be set as a link template. For example, if there exists an airflow config such as:

AIRFLOWTRACESBUTTON_LINK=View Trace in Honeycomb|https://ui.honeycomb.io/{env.team}/environments/{env.env}/datasets/{env.dataset}/trace?trace_id={trace_id}&span={span_id}&trace_start_ts={trace_start}&trace_end_ts={trace_end}

will allow button to appear in the extra links that will have "View Trace in Honeycomb" (example:)

that will redirect to the Honeycomb's UI.

Supported 'variable' could be

trace_id : id of the trace for the current DAG run
span_id : id of the span for the current task instance
trace_start : UNIX epoch timestamp (in seconds) of when the trace started
trace_end : UNIX epoch timestamp (in seconds) of when the trace ended
env.* : any value defined as environment variable (e.g. env.team=MYTEAM )

variables are enclosed with { } to denote it. in order to scape the '{' '}' character, simply use '{{' and '}}'.

howardyoo / airflow_otel_provider

feature: support of link button for the observability backend (for task instances) #8