Enable filtering within array elements of json docs

[islamaliev]

func TestJSONArrayIndex_WithNestedArraysAndObjects_ShouldScopeIndexSearch(t *testing.T) {
	req := `query {
		User(filter: {custom: {numbers: {nested: {_any: {_eq: 4}}}}}) {
			name
		}
	}`
	test := testUtils.TestCase{
		Actions: []any{
			testUtils.SchemaUpdate{
				Schema: `
					type User {
						name: String 
						custom: JSON @index
					}`,
			},
			testUtils.CreateDoc{
				DocMap: map[string]any{
					"name": "John",
					"custom": map[string]any{
						"numbers": []any{3, 5, map[string]any{"nested": []int{9, 4}}, 7},
					},
				},
			},
			testUtils.CreateDoc{
				DocMap: map[string]any{
					"name": "Islam",
					"custom": map[string]any{
						// there is sought value here, but not in "nested" scope
						"numbers": []any{4, 9, map[string]any{"nested": []int{0, 3}}},
					},
				},
			},
			testUtils.CreateDoc{
				DocMap: map[string]any{
					"name": "Islam",
					"custom": map[string]any{
						"numbers": []any{1, map[string]any{"another": []int{4, 3}}},
					},
				},
			},
			testUtils.Request{
				Request: req,
				Results: map[string]any{
					"User": []map[string]any{
						{"name": "John"},
					},
				},
			},
			testUtils.Request{
				Request:  makeExplainQuery(req),
				Asserter: testUtils.NewExplainAsserter().WithIndexFetches(1),
			},
		},
	}

	testUtils.ExecuteTestCase(t, test)
}

The test is specific for secondary indexes, but by removing couple things can be made regular.
Whoever picks up this task please also add secondary index somewhere here tests/integration/index/json_array_test.go if it's not too much trouble. Otherwise please create another task for sec. index.

Update:
After discussing with the team we concluded that we want queries to be more specific on what indexes of array we want to filter.
Proposed syntaxes were:

filter: {custom: {numbers: {2: {nested: {_any: {_eq: 4}}}}}}

filter: {custom: {numbers: {at: {index: 2, nested: {_any: {_eq: 4}}}}}}