created extra class and method for the issue in dp_engine.py

[prasanna7codes]

Description

Summary of Changes:
1)Dimensions Class:
Allows users to define partitions using dimensions.
Includes a method to compute the Cartesian product of the dimensions.

2)Integration with aggregate Method:
Checks if public_partitions is a Dimensions object.
Computes the Cartesian product of the dimensions before processing.

3)Helper Method:
_generate_cartesian_product generates the Cartesian product of the Dimensions object.

Affected Dependencies

import functools
from typing import Any, Callable, Optional, Sequence, Tuple, Union

import pipeline_dp
from pipeline_dp import budget_accounting
from pipeline_dp import combiners
from pipeline_dp import contribution_bounders
from pipeline_dp import dp_computations
from pipeline_dp import partition_selection
from pipeline_dp import pipeline_functions
from pipeline_dp import report_generator
from pipeline_dp import sampling_utils
from pipeline_dp.dataset_histograms import computing_histograms
from pipeline_dp.pipeline_backend import PipelineBackend
from pipeline_dp.private_contribution_bounds import PrivateL0Calculator

import itertools
import dataclasses
from typing import Any, Callable, Tuple
import numpy as np

import pipeline_dp
from pipeline_dp import combiners
import pipeline_dp.report_generator as report_generator

import pydp.algorithms.partition_selection as partition_selection # type: ignore

How has this been tested?

• Describe the tests that you ran to verify your changes.
• Provide instructions so we can reproduce.
• List any relevant details for your test configuration.

Checklist

• [] I have followed the Contribution Guidelines and Code of Conduct
• [] I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests