Add support for GitHub Enterprise

[yamao-latte]

Description

When the provider is set to 'github', the current implementation fails to correctly parse URLs from GitHub Enterprise Server instances. This causes errors when users attempt to use Enterprise Server URLs with our system.

Current Behavior

• URLs from github.com are parsed correctly
• URLs from GitHub Enterprise Server instances throw an error or are parsed incorrectly

Expected Behavior

• Both github.com and GitHub Enterprise Server URLs should be parsed correctly when the provider is set to 'github'

Steps to Reproduce

1. Set the provider to 'github'
2. Attempt to use a URL from a GitHub Enterprise Server instance (e.g., https://github.mycompany.com/org/repo/pull/123)
3. Observe the error or incorrect parsing

Proposed Solution

Update the URL parsing logic to accommodate both github.com and GitHub Enterprise Server URL structures. This may involve:

• Using more flexible regex patterns
• Adjusting the logic to handle varying URL formats
• Ensuring that repository names and PR/issue numbers are correctly extracted regardless of the exact URL structure

Additional Notes

This issue is related to the recent changes made in the PR and issue URL parsing functions. While those changes improved the situation, they didn't fully address the Enterprise Server use case.