Add `DataType` enum to `AttributeType`

The enum describes the type of the data stored for the attritbute type.
The data type can be: country, date, etc.

Bug: 393318914
Change-Id: I72035b51cbfb9c2d6f51c8af9e29b3431f320330
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6348861
Commit-Queue: Theo Cristea <theocristea@google.com>
Reviewed-by: Jan Keitel <jkeitel@google.com>
Cr-Commit-Position: refs/heads/main@{#1432045}