Add base class for upcoming object persistence operation-specific config objects

[ashovlin]

Description

This is adding a base class to use for the new set of operation-specific config objects for the object persistence APIs.

Motivation and Context

See #3376 for the full context for this change, this PR came from #3376 (comment). I'd rather merge this into the feature branch quickly, then rebase the PRs that are introducing the derived classes on top of it.

Testing

Existing DynamoDBv2 sln tests pass.

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)

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

License

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