chore: remove default values and replace with null to use upstream default settings

[bryantbiggs]

Description

• remove default values and replace with null to use upstream default settings

Motivation and Context

• the default values provided by the AWS provider/API will change periodically. instead of hard-coding those values in this module as the module default values, switching to null will allow the module to be flexible and change with the upstream source as needed

Closes #235
Closes #273

Breaking Changes

• No

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects
• tested using complete-postgresql - no diff change between master and this PR

[antonbabenko]

v2.30.0 has been just released.

[github-actions]

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