Make it possible to filter based on a nested field

[remiremi]

With this fix you could have a list filter that filters on a nested object field, for example doing

const ProductListFilter = (props: any) => (
  <Filter {...props}>
    <SelectInput
      label="Status"
      source="category.status"
      choices={[
        { id: "in_production", name: "In Production" },
        { id: "planned", name: "Planned" },
        { id: "retired", name: "Retired" }
      ]}
      emptyText="All"
      alwaysOn
    />
  </Filter>
);

export const ProductList = (props: any) => (
  <List
    {...props}
    filters={<ProductListFilter />}
    sort={{ field: "planting_date", order: "ASC" }}
    filterDefaultValues={{ category: { status: "in_production" } }}
  >
    .....

[pankgeorg]

Good job@remiremi! Thank you for that, I wanted exactly the same feature. Though, I think something in this PR seems wrong; the generated query for category.status@_ilike is {category: {"status@_ilike": {_eq: <value>}}} and not {category: {"status": {_ilike: <value> }}}

[pankgeorg]

I do the same here, following a different path from your approach: #47

[praveenweb]

@remiremi - Thanks for the PR. This looks good. But as @pankgeorg mentioned, the query generation had a minor issue.

So I have merged #47 and closing this in favour of that.