[Feature]: Add timestamps and sorting by time to Dynamo entities

[Jiloc]

Feature: Add timestamps and sorting by time to Dynamo entities

1. Description

Deposits, Withdrawals, request updates, Chainstates, etc., are always created without a timestamp. To support better sorting and pagination, it would be good to have created_at and modified_at timestamps associated with them.

1.1 Context & Purpose

Providing timestamps will help signers handle with pagination of requests.

2. Technical Details:

• Add created_at and modified_at fields to all relevant entities (e.g., Deposits, Withdrawals, Updates, Chainstates).
• Ensure modified_at is updated whenever an entity is modified.
• Support sorting and pagination of all deposits and withdrawal endpoints using the new timestamp fields.
• Migration: Assign timestamps to all existing entities in the database. At minimum, assign the timestamp of the associated Stacks block to created_at.

2.1 Acceptance Criteria:

• created_at and modified_at timestamps are added to all relevant entities.
• Timestamps are correctly set and updated in all relevant operations.
• Existing entities in the database have created_at populated with the timestamp of the associated Stacks block.
• Sorting and pagination by timestamps are supported and tested.

3. Related Issues and Pull Requests (optional):

#1148