Add __version__ support

[LakshmanKishore]

Summary: I have made the following changes to improve version management in the hdbscan project:

• Created a new file named version.py in the hdbscan folder.
• Defined a constant VERSION within version.py to store the version of the package.
• Updated the version management approach to use version.py for version information.

Details: In the past, the version of the hdbscan package used to be updated directly in the setup.py file. With these changes, we now store the version in the version.py file, which is accessible in both the __init__.py and setup.py files. This approach follows the common Python practice of managing the version in a dedicated file for improved consistency and ease of access.

Expected Behavior: After this change, the version of the hdbscan package can be consistently accessed from version.py and can be easily imported into other parts of the project, including the __init__.py and setup.py files. Users can now access the package version using hdbscan.__version__.

[LakshmanKishore]

Dear maintainers,

I kindly request that you consider tagging this contribution with the 'hacktoberfest-accepted' label or adding the 'hacktoberfest' topic to the repository. This would make it easier for participants in Hacktoberfest to find and contribute to this project.

Thank you!