Replace AttributesToGet usage with ProjectionExpression for batch get requests

[irina-herciu]

Replace AttributesToGet usage with ProjectionExpression for batch get requests created from the DynamoDB data model layer, and add tests around DocumentBatchGet behavior.

Description

• pass ProjectionExpression from ItemStorageConfig into DocumentBatchGet
• build projection expressions and expression attribute names as properties are added to storage config, (AttributesToGet internal property can be removed after PR#4343 is also merged)
• update request creation to use either ProjectionExpression or AttributesToGet, and throws if both are set,
• add unit tests for multi-batch execution and edge cases in DocumentBatchGet.

Motivation and Context

Replace legacy params usage in HLL

Testing

Unit tests added, all existing integration tests passing

Dry-runs

• DotNet Dry-run ID:
  • Pending
  • Completed successfully
  • Failed
• PowerShell Dry-run ID:
  • Pending
  • Completed successfully
  • Failed

Breaking Changes Assessment

1. Identify all breaking changes including the following details:
   • What functionality was changed?
   • How will this impact customers?
   • Why does this need to be a breaking change and what are the most notable non-breaking alternatives?
   • Are best practices being followed?
   • How have you tested this breaking change?
2. Has a senior/+ engineer been assigned to review this PR?

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)

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

[dscpinheiro]

Is this the same as #4343? (And if yes, should that PR be closed?)

[irina-herciu]

this PR targets BatchGet operations, and #4343 is for load item operation.

there is indeed code duplication as I needed to build and pass ProjectionExpression from ItemStorageConfig