Fix notify_only_default_branch check for Slack service
What does this MR do?
Fixes the notify_only_default_branch conditional check
Are there points in the code the reviewer needs to double check?
Why was this MR needed?
The notify_only_default_branch property is using boolean_accessor this means we need to check it using a question methods. Also add specs for disabling this option.
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Documentation created/updated
- API support added
- Added for this feature/bug
- All builds are passing
- Conform by the merge request performance guides
- Conform by the style guides
Branch has no merge conflicts with
master(if it does - rebase it please)
- Squashed related commits together