Fix local server_side_encryption_configuration with missing bucket_key_enabled

When explicitly setting server_side_encryption_configuration when using the module, I'm encountering this error:

Here is the configuration I've set:

server_side_encryption_configuration = {
    rule = {
      apply_server_side_encryption_by_default = {
        sse_algorithm     = "aws:kms"
        kms_master_key_id = module.s3_data_stores_kms_keys[each.key].key_arn
      }
      bucket_key_enabled = true
    }
  }

Defining in local.server_side_encryption_configuration a default for bucket_key_enabled should fix this error.