Introduce SettableWatcher to make writing Watcher related integration…

[imasahiro]

… test more easily

[codecov[bot]]

Codecov Report

Merging #693 (7490497) into master (8a32763) will decrease coverage by 0.13%. The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #693      +/-   ##
============================================
- Coverage     70.19%   70.06%   -0.14%     
+ Complexity     3419     3414       -5     
============================================
  Files           349      350       +1     
  Lines         13468    13487      +19     
  Branches       1454     1457       +3     
============================================
- Hits           9454     9449       -5     
- Misses         3133     3154      +21     
- Partials        881      884       +3     

Impacted Files	Coverage Δ
...linecorp/centraldogma/testing/SettableWatcher.java	0.00% <0.00%> (ø)
...erver/internal/storage/PurgeSchedulingService.java	70.11% <0.00%> (-6.90%)	:arrow_down:
...ient/armeria/legacy/LegacyCentralDogmaBuilder.java	81.48% <0.00%> (-3.71%)	:arrow_down:
...internal/storage/DirectoryBasedStorageManager.java	63.31% <0.00%> (-0.88%)	:arrow_down:
...internal/replication/ZooKeeperCommandExecutor.java	78.41% <0.00%> (+0.36%)	:arrow_up:
...centraldogma/server/internal/api/WatchService.java	79.66% <0.00%> (+3.38%)	:arrow_up:

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