[New Scheduler] Add a centralized watcher for etcd data

[jiangpengcheng]

Description

The FPC scheduler will use etcd to store and share some data, and some components need to get noticed for some data when they are changed(inserted, updated or removed), this PR implements a centralized watcher for them, which will watch all changes on etcd and distribute them to subscribers

design document: https://cwiki.apache.org/confluence/display/OPENWHISK/WatcherService

Related issue and scope

• I opened an issue to propose and discuss this change (#????)

My changes affect the following components

• API
• Controller
• Message Bus (e.g., Kafka)
• Loadbalancer
• Scheduler
• Invoker
• Intrinsic actions (e.g., sequences, conductors)
• Data stores (e.g., CouchDB)
• Tests
• Deployment
• CLI
• General tooling
• Documentation

Types of changes

• Bug fix (generally a non-breaking change which closes an issue).
• Enhancement or new feature (adds new functionality).
• Breaking change (a bug fix or enhancement which changes existing behavior).

Checklist:

• I signed an Apache CLA.
• I reviewed the style guides and followed the recommendations (Travis CI will check :).
• I added tests to cover my changes.
• My changes require further changes to the documentation.
• I updated the documentation where necessary.

[codecov-io]

Codecov Report

Merging #5069 (eb62d01) into master (4a13303) will decrease coverage by 53.36%.
The diff coverage is 89.58%.

@@             Coverage Diff             @@
##           master    #5069       +/-   ##
===========================================
- Coverage   81.72%   28.36%   -53.37%     
===========================================
  Files         210      204        -6     
  Lines       10167     9950      -217     
  Branches      440      447        +7     
===========================================
- Hits         8309     2822     -5487     
- Misses       1858     7128     +5270     

Impacted Files	Coverage Δ
...apache/openwhisk/core/service/WatcherService.scala	89.58% <89.58%> (ø)
.../main/scala/org/apache/openwhisk/utils/Retry.scala	0.00% <0.00%> (-100.00%)	⬇️
...n/scala/org/apache/openwhisk/utils/JsHelpers.scala	0.00% <0.00%> (-100.00%)	⬇️
...a/org/apache/openwhisk/common/ConfigMapValue.scala	0.00% <0.00%> (-100.00%)	⬇️
...g/apache/openwhisk/common/ResizableSemaphore.scala	0.00% <0.00%> (-100.00%)	⬇️
...pache/openwhisk/http/LenientSprayJsonSupport.scala	0.00% <0.00%> (-100.00%)	⬇️
.../apache/openwhisk/core/controller/Namespaces.scala	0.00% <0.00%> (-100.00%)	⬇️
...pache/openwhisk/core/controller/CorsSettings.scala	0.00% <0.00%> (-100.00%)	⬇️
...che/openwhisk/core/entitlement/RateThrottler.scala	0.00% <0.00%> (-100.00%)	⬇️
...he/openwhisk/core/entitlement/KindRestrictor.scala	0.00% <0.00%> (-100.00%)	⬇️
... and 155 more

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[style95]

This is given from #5063

[style95]

Suggested change

	case class UnWatchEndpoint(watchKey: String, isPrefix: Boolean, watchName: String, needFeedback: Boolean = false)
	case class UnwatchEndpoint(watchKey: String, isPrefix: Boolean, watchName: String, needFeedback: Boolean = false)

[ningyougang]

LGTM

[KeonHee]

Referring to review #5068 (review), you need to add org/apache/openwhisk/core/service/** to REQUIRE_SCHEDULER to run the test in CI .

[bdoyle0182]

LGTM