BulkInsertAsync with SqlBulkCopyOptions.KeepIdentity inserts NULLs instead of provided IDs

[Bigfellahull]

When performing a bulk insert with SqlBulkCopyOptions.KeepIdentity, the expected behaviour is that IDs provided in the entity list should be inserted as-is. However, due to how default values are handled in InnerGetDataTable, NULLs are inserted instead, leading SQL Server to generate new IDs.

Steps to Reproduce:

• Create an entity with a GUID primary key.
• Populate a list of entities with pre-generated IDs.
• Call BulkInsertAsync with KeepIdentity:

var bulkConfig = new BulkConfig
{
    SqlBulkCopyOptions = SqlBulkCopyOptions.KeepIdentity
};
await dbContext.BulkInsertAsync(documents, bulkConfig);

• Observe that SQL Server generates new IDs instead of using the provided ones.

Expected Behaviour:
The provided IDs should be inserted into the identity column.

Actual Behaviour:
NULLs are inserted instead, causing SQL Server to generate new IDs.

Root Cause:
The logic in InnerGetDataTable excludes columns with default values during insert

var hasDefaultValueOnInsert = tableInfo.BulkConfig.OperationType == OperationType.Insert
    && !tableInfo.BulkConfig.SetOutputIdentity
    && tableInfo.DefaultValueProperties.Contains(property.Name);

Proposed Fix:
Modify hasDefaultValueOnInsert to check for KeepIdentity before excluding default value columns:

var hasDefaultValueOnInsert = tableInfo.BulkConfig is { OperationType: OperationType.Insert, SetOutputIdentity: false }
    && tableInfo.DefaultValueProperties.Contains(property.Name)
    && !tableInfo.BulkConfig.SqlBulkCopyOptions.HasFlag(SqlBulkCopyOptions.KeepIdentity);

This ensures the ID column is included when KeepIdentity is specified.