Implement non-admin account management features in journalist API

[redshiftzero]

Description

The plan is to eventually deprecate the journalist web interface (except the API), leaving only the client application. As such, all functionality available via the journalist web interface must be possible via the API.

A (non-admin) journalist user can use the journalist web interface to cycle their password and 2FA. This ticket is to add this non-admin journalist account management functionality to the API.

User Stories

As a journalist user, I want to be able to change my account details in the securedrop-client program so that I can cycle my credentials if needed.