Support for half year

[stugr]

I was able to add support for half years by using quarter year as a guide to add the relevant code - it would be good if this code was added to the official timeline visual as it's a pretty quick and easy enhancement

https://github.com/stugr/powerbi-visuals-timeline

[helen508light]

@stugr please create PR
Requirements for PRs are all test pass and test coverage for new feature\fix
Our team should review it