update Mutation: push to Array instead of replacing it.

Let's say I have a Schema like this:
```js
const mySchema = new Schema({
foo: [{ type: String }]
}]
```

And I want to update an existing Document - from what I know currently we only have the option to replace our fields with new ones. Are there any options to

1. Push certain elements to a field
2. Pop certain elements from a field

Example push:
I have a document
```js
{
foo: [ "a", "b", "c"]
}
```
and want to add `"d"` to the array.

Currently I would need to
- Query the document to get foo
- Create a new array
- Mutate the document with the new array

which would cost many recources

_or_

- Create a custom Mutation that pushes instead of updates

which I see problematic if we have Schemas with multiple arrays and we want to allow mutations like
- update Array1
- replace Array2

Same Problems exist with popping elements.

I think it would be great if we had some kind of options in the Mutation itself. It would be super neat if we had a syntax that allows stuff like this:
```js
{
_id: "6099cb18f294f83dbcbf8936",
foo: ["blue"],
bar: ["dolores"],
xyz: ["deleteThis", "butNotThat"],
}
```
```graphql
mutation {
somethingUpdateById(
_id: "6099cb18f294f83dbcbf8936"
record: {
foo: ["green", "yellow"]
bar: ["Lorem", "Ipsum"]
xyz: ["deleteThis"]
}
options: {
arrays: {
foo: replace
bar: push
xyz: pop
}
}
}) {
record {
foo
bar
xyz
}
}
}
```
```js
#response
{
foo: ["green", "yellow"]
bar: ["dolores", "Lorem", "Ipsum"]
xyz: ["butNotThat"]
}
```

I know this is asking for extremely much, but perhaps I inspire someone to implement something like it. My skills unfortunately aren't high enough to do it myself.