Add endpoint that combines user profile update and user fi association

[lchen-2101]

Parent ticket or topic: cfpb/sbl-project#17

Context

Currently the API supports user profile update and user fi association separately, we would like to add an endpoint that combines the 2 functionalities.

Task

Create DTO to restrict the request schema, currently it's free form KV map; add endpoint that takes in the new DTO which contains payload for both user profile (first name, last name), and fi associations.

Acceptance criteria

• DTO for API created
  • body should look like

    {
      "first_name": "First",
      "last_name": "Last",
      "leis": ["LEI1", "LEI2"]
    }

• API endpoint added.