Update Mock Server for user updates

[adamwhitlock1]

User Story

As a frontend engineer I want to enable research participants to update the mock information that is present from prefill on out research tasks with any new content that they so choose.

Background

For the first pattern we gave users a new address or new phone number to update the forms with, and that sometimes led to some confusion.

ACs

• [x] Create an in memory database that allows semi-ephemeral updates to the user object.
• [x] Updates to mailing address, home address, mobile phone, home phone, and email address should be supported
• [x] When the server restarts, ensure that the user object returns to the original state

[adamwhitlock1]

Work has been completed and is in PR https://github.com/department-of-veterans-affairs/vets-website/pull/32101