Rename OutputTimeFn.OUTPUT_AT_MAX to OUTPUT_AT_LATEST for clarity

----Release Notes----
[]
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117973512

Author: charlesccychen

google/cloud/dataflow/transforms/trigger_transcripts.yaml

@@ -41,7 +41,7 @@ transcript:
 name: output_time_fn_latest
 window_fn: FixedWindows(10)
 trigger_fn: Default
-output_time_fn: OUTPUT_AT_MAX
+output_time_fn: OUTPUT_AT_LATEST
 transcript:
   - input: [1, 2, 3, 10, 11, 25]
   - watermark: 100

google/cloud/dataflow/transforms/window.py

@@ -60,7 +60,7 @@ class OutputTimeFn(object):
 
   OUTPUT_AT_EOW = 'OUTPUT_AT_EOW'
   OUTPUT_AT_EARLIEST = 'OUTPUT_AT_EARLIEST'
-  OUTPUT_AT_MAX = 'OUTPUT_AT_MAX'
+  OUTPUT_AT_LATEST = 'OUTPUT_AT_LATEST'
   OUTPUT_AT_EARLIEST_TRANSFORMED = 'OUTPUT_AT_EARLIEST_TRANSFORMED'
 
   @staticmethod
@@ -69,7 +69,7 @@ def get_impl(output_time_fn, window_fn):
       return timeutil.OutputAtEndOfWindowImpl()
     elif output_time_fn == OutputTimeFn.OUTPUT_AT_EARLIEST:
       return timeutil.OutputAtEarliestInputTimestampImpl()
-    elif output_time_fn == OutputTimeFn.OUTPUT_AT_MAX:
+    elif output_time_fn == OutputTimeFn.OUTPUT_AT_LATEST:
       return timeutil.OutputAtLatestInputTimestampImpl()
     elif output_time_fn == OutputTimeFn.OUTPUT_AT_EARLIEST_TRANSFORMED:
       return timeutil.OutputAtEarliestTransformedInputTimestampImpl(window_fn)