[WIP] [Workflow Interface] Refactor FLSpec and Runtime to enhance modularity

[ishant162]

Background
Proposal: #1317

Change Description

• Updates to FLSpec, LocalRuntime, FederatedRuntime and Aggregator classes.
• Shift the run() method implementation from FLSpec to Runtime.
• Runtime now passes collaborator information to FLSpec, enabling foreach operations, necessitating changes to the execution flow.
• Updated WorkspaceExport functionality to align with the refactor changes.

Verification

• Verified all testcases from tests/github/experimental/workflow/LocalRuntime.
• Verified all testcases from tests/github/experimental/workflow/FederatedRuntime.
• Verified Tutorials 101_MNIST of LocalRuntime and FederatedRuntime.

File Modifications

• openfl-tutorials/experimental/workflow/101_MNIST.ipynb
• openfl-tutorials/experimental/workflow/FederatedRuntime/101_MNIST/workspace/101_MNIST_FederatedRuntime.ipynb
• openfl/experimental/workflow/component/aggregator/aggregator.py
• openfl/experimental/workflow/interface/fl_spec.py
• openfl/experimental/workflow/runtime/federated_runtime.py
• openfl/experimental/workflow/runtime/local_runtime.py
• openfl/experimental/workflow/utilities/runtime_utils.py
• openfl/experimental/workflow/workspace_export/export.py
• All testcases from tests/github/experimental/workflow/LocalRuntime.
• All testcases from tests/github/experimental/workflow/FederatedRuntime.

Changelog:

• FLSpec Refactor.
• LocalRuntime Refactor.
• Update LocalRuntime Tutorial (101_MNIST) & Testcases.
• FederatedRuntime Refactor.
• Update FederatedRuntime Tutorial (101_MNIST) & Testcases.

Note:
Following changes will be done in a follow-up PR:

• Remaining LocalRuntime & FederatedRuntime Tutorials.