Adding support for external commits in referenced events

[Leo-Send]

External commits that mention issues in the project can now be fetched. They receive a new type of related commit, called commitReferencesIssueExternal. Also fixed hashatags in markdown code environments incorrectly registering as references to other issues/PRs.

[Copilot]

Pull Request Overview

This PR adds support for external commits in referenced events, allowing commits from external repositories that mention issues to be properly tracked. It also fixes a bug where hashtags in markdown code blocks were incorrectly interpreted as issue/PR references.

Key changes:

• External commits now receive a distinct type (commitReferencesIssueExternal) to differentiate them from internal repository commits
• Markdown code blocks (delimited by triple backticks) are now excluded when parsing hashtag references
• Enhanced error handling and logging for commit retrieval failures

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
IssueDataProcessor.java	Added logic to differentiate external commits and filter out hashtags within markdown code blocks
GitHubRepository.java	Implemented new method to fetch commits via URL for external references with improved error logging
GitHubCommit.java	Added isExternal field and accessor methods to track external commit status
EventDataProcessor.java	Enhanced commit retrieval to fallback to URL-based fetching for external commits
README.md	Added documentation explaining referenced events behavior and known limitations

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