Replace (or remove) `id` field description about odmantic

[Olegt0rr]

Solution to hide this description described in #75 (comment)
But I'm still suggesting to remove current description as I wrote above

[Olegt0rr]

Bad news, it's not a solution.

id: ObjectId = Field(primary_field=True, description='My ID') is overwrited by MongoDB ObjectId string description :(

[adeelsohailahmed]

Bad news, it's not a solution.

My solution was specific to that issue. The user wanted to use their own strings for id field for their model instead of letting ODMantic generate id itself.

[art049]

Replacing the default example is totally good to me.
We can as well remove the default description.

What kind of database and what kind of identifier generation are used to store the data is not a client's business.

Unfortunately, it's a bit linked. Since we perform ObjectId validation, passing an invalid id (like a non hex string) will raise a validation error.

We can still remove the description since it's overriding everything right now though.