Add YAMLConfigManager support

[niveathika]

Purpose

$subject fixes #1445

Goals

To support YAML Config Manager for easy setting of system properties in SiddhiManager

Approach

As in f3c8ea2

Release note

Add support YAML Config Manager for easy setting of system properties in SiddhiManager through a YAML file

Automation tests

• Unit tests - Attached herewith
• Integration tests - N/A

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? yes
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes

Test environment

1.8.0_191

[codecov-io]

Codecov Report

Merging #1446 into master will increase coverage by <.01%.
The diff coverage is 73%.

@@             Coverage Diff              @@
##             master    #1446      +/-   ##
============================================
+ Coverage     67.75%   67.76%   +<.01%     
  Complexity       41       41              
============================================
  Files           634      643       +9     
  Lines         26792    26892     +100     
  Branches       4232     4241       +9     
============================================
+ Hits          18154    18224      +70     
- Misses         6868     6891      +23     
- Partials       1770     1777       +7

Impacted Files	Coverage Δ	Complexity Δ
...dhi/core/exception/YAMLConfigManagerException.java	0% <0%> (ø)	0 <0> (?)
...va/io/siddhi/core/util/config/model/Extension.java	100% <100%> (ø)	0 <0> (?)
...a/io/siddhi/core/util/config/YAMLConfigReader.java	100% <100%> (ø)	0 <0> (?)
...ddhi/core/util/config/model/RootConfiguration.java	100% <100%> (ø)	0 <0> (?)
...va/io/siddhi/core/util/config/model/Reference.java	100% <100%> (ø)	0 <0> (?)
.../src/main/java/io/siddhi/core/util/FileReader.java	35.71% <35.71%> (ø)	0 <0> (?)
.../io/siddhi/core/util/config/YAMLConfigManager.java	80% <80%> (ø)	0 <0> (?)
...util/config/model/ReferenceChildConfiguration.java	87.5% <87.5%> (ø)	0 <0> (?)
...util/config/model/ExtensionChildConfiguration.java	87.5% <87.5%> (ø)	0 <0> (?)
.../siddhi/core/util/event/handler/StreamHandler.java	62% <0%> (-12%)	0% <0%> (ø)
... and 12 more

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