fix(plugin-ecommerce): variant creation blocked by variants in trash (#15449)

### What?

This PR fixes a type error that prevents variant creation in the admin
panel when there is any variant currently in the trash

### Why?

When a variant is added, variants that are in the trash are included in
the query, but these are not populated, which causes a type error when
the variant.options array is accessed with a `.length` call.

Once there is a variant in the trash, adding new variants will always
throw an error.

### How?

By editing the query to filter deleted variants:
```ts
where {
  deletedAt: { exists: false },
```

Fixes #15448 

https://discord.com/channels/967097582721572934/1465838361561403516

### Comments

Perhaps the type for `variant` could also be narrowed in this function,
as it is currently `any`. Something like
`variant: { options: DefaultDocumentIDType[] }`

---------

Co-authored-by: Colum Kelly <columk1@users.noreply.github.com>