Support passing a custom truststore with central calls

[azinneera]

Purpose

Support passing a custom truststore with central calls

Approach

A custom truststore path can be set with the below environment variables:
BALLERINA_CA_BUNDLE
BALLERINA_CA_PASSWORD
BALLERINA_CA_CERT

Check List

• Read the Contributing Guide
• Updated Change Log
• Checked Tooling Support (#)
• Added necessary tests
  • Unit Tests
  • Spec Conformance Tests
  • Integration Tests
  • Ballerina By Example Tests
• Increased Test Coverage
• Added necessary documentation
  • API documentation
  • Module documentation in Module.md files
  • Ballerina By Examples

[codecov]

Codecov Report

Attention: Patch coverage is 59.45946% with 15 lines in your changes missing coverage. Please review.

Please upload report for BASE (2201.11.0-stage@c4c87cb). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ballerinalang/central/client/CentralAPIClient.java	59.45%	13 Missing and 2 partials ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##             2201.11.0-stage   #43621   +/-   ##
==================================================
  Coverage                   ?   77.40%           
  Complexity                 ?    58583           
==================================================
  Files                      ?     3445           
  Lines                      ?   219080           
  Branches                   ?    28962           
==================================================
  Hits                       ?   169568           
  Misses                     ?    40093           
  Partials                   ?     9419           

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