[VMS] Modify donation schema to include user-id

[PC98]

• Let's establish a one-to-one relationship between donations and User IDs.
• However certain donations can have a null user ID.
• Make modifications to the logDonation server action and request to support user ID. Right now, the front-end code can pass null as the user ID but let's add a TODO saying that this should be changed.
• No need for a migration script since we don't have any existing donations in our DB.