Add support for branch names, PR URLs, and related Smart Values

[isemenovdev]

Hi team,

I’ve been using the GitHub for Jira integration and noticed that it would be incredibly helpful to include more detailed information in Slack notifications. Currently, it seems like the available Smart Values (e.g., {{customfield_10000}}) are limited, and adding more context would reduce the need to switch between tools.

For example, it would be great to include details like:

PR: <{{pullRequest.url}}|{{pullRequest.title}}>  
Issue: <{{issue.url}}|{{issue.key}}>  
Branch: {{branch.name}}  
Commit messages: {{commit.message}}  
Repository: {{repository.name}}  

This would make it easier for teams to quickly understand the context of a notification and take action.