feat: add GitHub issue actions

[snobbee]

Follow up on #96 to merge into sif-dev brannch

I'll help fill out the PR template based on the changes shown in the files.

Relates to:

plugin-github

Risks

Low - These changes add new GitHub issue management functionality through well-defined APIs

Background

What does this PR do?

Adds three new GitHub plugin actions for issue management:

• CREATE_ISSUE: Creates new issues in GitHub repositories
• MODIFY_ISSUE: Updates existing issues (title, body, state, labels)
• ADD_COMMENT_TO_ISSUE: Adds comments to existing issues

What kind of change is this?

Features (non-breaking change which adds functionality)

Documentation changes needed?

My changes require a change to the project documentation to document the new issue management capabilities.

Testing

Where should a reviewer start?

1. Review the three new plugin files:

• packages/plugin-github/src/plugins/createIssue.ts
• packages/plugin-github/src/plugins/modifyIssue.ts
• packages/plugin-github/src/plugins/addCommentToIssue.ts

2. Review the corresponding schema definitions in:

• packages/plugin-github/src/types.ts
• packages/plugin-github/src/templates.ts

5. Verify error handling by testing with:

• Invalid repository details
• Non-existent issues
• Missing permissions

The changes include proper error handling and logging throughout the new functionality.