More granular omit options

**Is your feature request related to a problem? Please describe.**

Take a model like:

```prisma
model Person {
id String @id @default(cuid())
email String
firstname String
surname String
createdAt DateTime @default(now())
updatedAt DateTime @updatedAt
users User[]
}
```

This outputs all the fields in all the input types, meaning users can update the `createdAt` and `updatedAt` - which will be handled by Prisma.

If we use `/// @TypeGraphQL.omit(input: true)`, this omits the type from all inputs, including the `Where` inputs, so these fields cannot be used in where queries.

**Describe the solution you'd like**

It would be good to make the `omit` more granular, i.e. `/// @TypeGraphQL.omit(update: true)`, preventing the fields from being part of the `Update` inputs, but still allowing them to be part of the `Where` inputs.

**Describe alternatives you've considered**

Not sure if there are any, it's rather an all or nothing setting at the moment?

**Additional context**
Add any other context or screenshots about the feature request here.