Update an account in the service

[ImranullahKhann]

As a client application
I need to update details of an existing account
So that the account information remains current and accurate

Details and Assumptions

* Only specific fields may be updated (e.g., email, name, address)
* The service should validate the input data
* A success or error response must be returned

Acceptance Criteria

gherkin
Given an existing account and valid update data  
When I send a PUT request to the update endpoint  
Then the account is updated with the new data

Given invalid update data  
When I send a PUT request  
Then I receive a 400 Bad Request with validation errors