feat(profiling): Add insufficient data as client discard reason (#4407)

We'd like to add a new client discard reason called `insufficient_data` for the
use case where the SDK did not collect enough data for a valid profile and
discards it as a result.

snuba/datasets/processors/outcomes_processor.py

@@ -33,6 +33,7 @@
  "sample_rate",
  "send_error",
  "internal_sdk_error",
+ "insufficient_data",
  "backpressure",
  ]
 )