Feature: Add Deprecation Message

[MHHukiewitz]

Deprecation messages are displayed when either trying to use the now abstract classes AlephClient and AuthenticatedAlephClient in the form of either

• ImportError when imported directly from aleph.sdk
• or NotImplementedError when imported from their source files, with additional info about which classes to use instead.

[github-actions]

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The PR introduces a significant change to the Python SDK library for Aleph.im network. The changes involve major modifications in setup.cfg file which may affect other parts of the system that depend on this configuration, and also updates to the __init__.py file where it raises import errors for deprecated classes (AlephClient, AuthenticatedAlephClient, synchronous, asynchronous). This PR also introduces changes in several files under the 'src/aleph/sdk' directory which may affect other parts of the system that depend on these specific modules.

The changes are categorized as BLACK because they involve extensive changes to critical components and require deep understanding of the project architecture, including its dependencies and how it interacts with other systems. Only experienced developers should review this PR, as it involves significant architectural changes. The label 'BLACK' is used sparingly in this case, indicating that this PR requires a high level of expertise and attention to detail.

Please note that the categorization may not be 100% accurate due to the complexity of the changes involved. It's always recommended to review the code changes thoroughly before merging them into the main branch.