Behavior with aliases

Hello, I'm thinking to enable the aliases on the fields. It would enable a cleaner attribute validation to avoid conflicts between builtin methods and the fields for example (as already done by Pydantic).

The current behavior I'm thinking of:
- If a field has an `alias` and no `key_name`, the resulting document key will be the alias
- It's still possible to customize the key_name with an alias already set by specifying the `key_name` kwarg

Do you think some more customization/options would be useful ?

No file or test is identified; start by locating the model field alias and key_name handling and reviewing how fields become MongoDB document keys. Done would require a decided alias/key_name behavior, documented edge cases around builtin-name conflicts, and tests covering the selected rules.

Written by the indexing model from the issue text.