Add support to publish custom analytics data from APIM

[YasasRangika]

Purpose

To add support to publish custom analytics data from APIM by including any attributes to the existing event schema.

Goal

Fixes: wso2/api-manager#443

Approach

• Introduced new property: customProperties to the existing event schema.
• This property always includes apiContext and userName.
• Custom properties can be added following https://github.com/wso2/samples-apim/tree/master/analytics-custom-data-provider

[codecov]

Codecov Report

Merging #11349 (f779e0a) into master (b73dbf1) will decrease coverage by 2.23%.
The diff coverage is 7.93%.

@@             Coverage Diff              @@
##             master   #11349      +/-   ##
============================================
- Coverage     47.62%   45.38%   -2.24%     
+ Complexity     5186     4757     -429     
============================================
  Files          1740     1742       +2     
  Lines        124422   124620     +198     
  Branches      17046    17079      +33     
============================================
- Hits          59257    56562    -2695     
- Misses        58331    61300    +2969     
+ Partials       6834     6758      -76     

Flag	Coverage Δ
integration_tests	39.23% <7.93%> (-3.10%)	⬇️
unit_tests	20.39% <0.00%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
...on/analytics/collectors/AnalyticsDataProvider.java	0.00% <0.00%> (ø)
...cs/collectors/impl/FaultyRequestDataCollector.java	0.00% <0.00%> (ø)
...s/collectors/impl/SuccessRequestDataCollector.java	0.00% <0.00%> (ø)
.../apimgt/common/analytics/publishers/dto/Event.java	0.00% <0.00%> (ø)
...ay/handlers/analytics/AnalyticsMetricsHandler.java	0.00% <0.00%> (ø)
...n/apimgt/gateway/handlers/analytics/Constants.java	0.00% <ø> (ø)
...ndlers/analytics/SynapseAnalyticsDataProvider.java	0.00% <0.00%> (ø)
...ming/websocket/WebSocketAnalyticsDataProvider.java	0.00% <0.00%> (ø)
...ng/websocket/WebSocketAnalyticsMetricsHandler.java	0.00% <0.00%> (ø)
...pimgt/gateway/internal/ServiceReferenceHolder.java	71.53% <26.31%> (-7.23%)	⬇️
... and 160 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b73dbf1...f779e0a. Read the comment docs.