Type of span. Can be used to specify additional relationships
between spans in addition to a parent/child relationship.
Values:
SPAN_KIND_UNSPECIFIED (0):
Unspecified. Do NOT use as default.
Implementations MAY assume SpanKind.INTERNAL to
be default.
INTERNAL (1):
Indicates that the span is used internally.
Default value.
SERVER (2):
Indicates that the span covers server-side
handling of an RPC or other remote network
request.
CLIENT (3):
Indicates that the span covers the
client-side wrapper around an RPC or other
remote request.
PRODUCER (4):
Indicates that the span describes producer
sending a message to a broker. Unlike client and
server, there is no direct critical path latency
relationship between producer and consumer spans
(e.g. publishing a message to a pubsub service).
CONSUMER (5):
Indicates that the span describes consumer
receiving a message from a broker. Unlike client
and server, there is no direct critical path
latency relationship between producer and
consumer spans (e.g. receiving a message from a
pubsub service subscription).
