feat: StringList handling in default parameter processor

[Plazmius]

Description

Add handling for StringList parameters, which is a type of parameter, supported by AWS SSM

Motivation and Context

This addresses #48

Testing

I have run unit and integration tests and used this code in my project

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

While tests are passing, I think whoever is using DefaultParameterProcessor won't expect that StringList are now handled differently. However, I would expect that one of only three SSM parameters type would convert to collection automatically.

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

Not sure that this feature fits the current test structure, but old tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[BradKnowles]

Thank you for this! I used your code to create a custom StringListParameterProcessor, inheriting from DefaultParameterProcessor and it worked perfectly.

[ashishdhingra]

Changes work fine while adjusting and executing sample application in this repo. Sample data returned using Get endpoint:

{"settings":{"stringValue":"string-value","integerValue":10,"dateTimeValue":"2000-01-01T00:00:00","booleanValue":true,"timeSpanValue":"00:05:00","stringValues":["White","Yellow","Green","Black"]}}