Improve exceptions thrown when making DynamoDB queries using object-mapper programming model with DisableFetchingTableMetadata and missing index definitions

[ashovlin]

Description

• Throws exceptions when building DynamoDB queries for the object-mapper model when:
  1. DisableFetchingTableMetadata is true
  2. The table's hash and/or range keys are not accurately provided
• Updates some docs for DisableFetchingTableMetadata to match what we did in feat: Adds TableBuilder, which can be used to prepopulate the internal metadata cache used by the document and object-mapper DynamoDB programming models #3055
• Updates the code that builds a Table from the attributed class to support GSI's without a range key
  • This is implicitly tested by the new DisableFetchingTableMetadata_QueryWithMissingRangeKey_ThrowsException, though that throws an exception later in the code path.

Motivation and Context

DOTNET-7182 - we want to avoid any null reference or index out of range exceptions when accessing the SDK's internal cache of table metadata

Testing

• Added new tests assert our expected exception type for a few cases
• Existing net35/net45 DDB unit and integration tests pass locally

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 - still need to do an internal dry-run

License

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