[fix] Add base URL extraction method to GithubRepositoryReader and update version to 0.4.0

[elia-bracci-hs]

Description

This PR introduces a new method to extract the base URL from various types of GitHub blob URLs in the GithubRepositoryReader. The change addresses an issue where URL parsing resulted in incorrect base URLs for GitHub Enterprise domains, leading to inaccurate links when interacting with repositories hosted on custom or enterprise GitHub instances.

Changes

• New Method: Adds _get_base_url, a utility to correctly parse and extract the base URL from blob URLs. This method now properly handles both standard GitHub domains and custom GitHub Enterprise domains, as well as various edge cases.
• Testing: Includes a comprehensive set of unit tests to validate the URL extraction functionality, covering standard GitHub URLs, enterprise domains, and edge cases (e.g., malformed or empty URLs).
• Version Update: Increments the package version to 0.4.0

Fixes # (issue)

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran make format; make lint to appease the lint gods