fix jira override behaviour

[jonathanlam]

Description

If there is a global config file and repo config file, the repo config file is not overriding the global Jira settings. Only priorities and assignees were being overridden.

the fix allows project key, issue type etc to also be overriden if they are not empty strings

Checklist

• I have added one of the patch, minor, major or no-release labels
• I have linked an issue from this repository using the Development option
• I have performed a self-review of my own code
• I have checked for redundant or commented out code
• I have commented my code where I can't make it self-documenting
• I have made corresponding changes to the documentation
• I have added any appropriate tests