support Slack alarm hooks

[JaredTan95]

Please answer these questions before submitting a pull request

• Why submit this pull request?

• Bug fix

• New feature provided

• Improve performance

• Related issues
  closes Forward the alarm message to slack #5355

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Bug fix

• Bug description.

• How to fix?

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New feature or improvement

• Describe the details and related test reports.

[codecov]

Codecov Report

Merging #5364 into master will decrease coverage by 0.11%.
The diff coverage is 29.41%.

@@             Coverage Diff              @@
##             master    #5364      +/-   ##
============================================
- Coverage     53.24%   53.12%   -0.12%     
+ Complexity     3224     3218       -6     
============================================
  Files           827      831       +4     
  Lines         20875    20943      +68     
  Branches       2029     2032       +3     
============================================
+ Hits          11115    11127      +12     
- Misses         8850     8907      +57     
+ Partials        910      909       -1     

Impacted Files	Coverage Δ	Complexity Δ
.../server/core/alarm/provider/AlarmRulesWatcher.java	64.70% <0.00%> (-1.97%)	6.00 <0.00> (ø)
...ywalking/oap/server/core/alarm/provider/Rules.java	100.00% <ø> (ø)	1.00 <0.00> (ø)
...ap/server/core/alarm/provider/WebhookCallback.java	28.57% <16.66%> (ø)	2.00 <1.00> (ø)
...r/core/alarm/provider/slack/SlackhookCallback.java	23.25% <23.25%> (ø)	2.00 <2.00> (?)
...ng/oap/server/core/alarm/provider/RulesReader.java	53.62% <47.05%> (-5.31%)	3.00 <0.00> (ø)
.../oap/server/core/alarm/provider/NotifyHandler.java	97.91% <100.00%> (+0.02%)	17.00 <0.00> (ø)
.../core/logging/core/coverts/ThrowableConverter.java	18.18% <0.00%> (-63.64%)	2.00% <0.00%> (-2.00%)
...apm/agent/core/remote/ServiceManagementClient.java	73.58% <0.00%> (-9.44%)	10.00% <0.00%> (-1.00%)
...king/apm/agent/core/remote/GRPCChannelManager.java	56.41% <0.00%> (-8.98%)	12.00% <0.00%> (-3.00%)
...kywalking/apm/agent/core/jvm/JVMMetricsSender.java	82.35% <0.00%> (-8.83%)	11.00% <0.00%> (-1.00%)
... and 18 more

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Review comments are addressed

[kezhenxu94]

Fix the failed checks (because of logger naming issue), and the PR looks good to me

[wu-sheng]

@JaredTan95 Do you have a screenshot? I need one for twitter :)

[JaredTan95]

@JaredTan95 Do you have a screenshot? I need one for twitter :)

[wu-sheng]

Will post on Monday.