Maintenance: Refactor in `users` domain in `webserver`

[pcrespov]

web-server's users domain

• CSR layers
• review S and R interfaces
• schemas vs domains (rm common)
• review repository execution and result: one, one_or_none etc.

Database

• rename columns in models

users.id
users.name
users.first_name
users.last_name

So i guess I could move it to

users.id
users.user_name
users.first_name
users.last_name

Models

• Update = PATCH, Replace = PUT.
  In any case, I notice we get confused between update and replace. I guess it means we should perpahs start using Patch.

So the model names should be : $ResourceName$Operation where Operation in [Get, Update, Replace, Delete, Create]. Perhaps instead of Update we should use Patch?

Exception handling

• mappers

Originally posted by @pcrespov in #6904 (comment)