update/delete historical detector;search AD tasks

[ylwu-amzn]

Description of changes:

1. When user update historical detector, check if there is running task, and user can't switch between realtime and historical.
2. When user delete historical detector, check if there is running task.
3. Add. new search API to support searching AD tasks.

Test

1. ./gradlew build
2. ./gradlew integTest -PnumNodes=3
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[codecov]

Codecov Report

Merging #362 (f1cd3f0) into master (74230c5) will increase coverage by 0.03%.
The diff coverage is 55.44%.

@@             Coverage Diff              @@
##             master     #362      +/-   ##
============================================
+ Coverage     78.91%   78.94%   +0.03%     
- Complexity     2635     2651      +16     
============================================
  Files           243      247       +4     
  Lines         11658    11695      +37     
  Branches       1002     1006       +4     
============================================
+ Hits           9200     9233      +33     
- Misses         1984     1988       +4     
  Partials        474      474              

Flag	Coverage Δ	Complexity Δ
cli	79.27% <ø> (ø)	0.00 <ø> (ø)
plugin	78.92% <55.44%> (+0.03%)	0.00 <16.00> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ	Complexity Δ
...ndistroforelasticsearch/ad/task/ADTaskManager.java	72.58% <6.66%> (-2.42%)	79.00 <0.00> (ø)
...est/handler/IndexAnomalyDetectorActionHandler.java	49.19% <20.68%> (-3.49%)	32.00 <2.00> (+1.00)	⬇️
...ransport/DeleteAnomalyDetectorTransportAction.java	21.50% <36.36%> (-0.19%)	4.00 <1.00> (+1.00)	⬇️
...stroforelasticsearch/ad/model/AnomalyDetector.java	95.59% <50.00%> (-0.41%)	91.00 <0.00> (+3.00)	⬇️
...stroforelasticsearch/ad/AnomalyDetectorPlugin.java	95.48% <100.00%> (+0.06%)	11.00 <0.00> (ø)
...elasticsearch/ad/rest/RestSearchADTasksAction.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)
...transport/IndexAnomalyDetectorTransportAction.java	73.52% <100.00%> (+0.80%)	11.00 <0.00> (ø)
...lasticsearch/ad/transport/SearchADTasksAction.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)
...rch/ad/transport/SearchADTasksTransportAction.java	100.00% <100.00%> (ø)	2.00 <2.00> (?)
...ransport/SearchAnomalyDetectorTransportAction.java	100.00% <100.00%> (+51.61%)	2.00 <1.00> (-2.00)	⬆️
... and 13 more