ActivityLink
Activity may be linked to zero or more other ActivityContext that are causally related.
Links can point to ActivityContexts inside a single Trace or across different Traces.
Links can be used to represent batched operations where a Activity was initiated by multiple initiating Activities,
each representing a single incoming item being processed in the batch.
Retrieve the ActivityContext object inside this ActivityLink object.
Retrieve the key-value pair list of tags attached with the ActivityContext.
Construct a new ActivityLink object which can be linked to an Activity object.