Enhance sample plugin with Jest Unit Test

[woelfle]

In order to be able to guard custom obsidian plugins with unit tests, it'd be great if the sample plugin would already contain an initial Jest Unit Test and the package.json configured to execute it.

[andymac4182]

This would be great :)

[hjonasson]

@woelfle @andymac4182 and 👍 people. I created a PR here as this seemed a requested feature. @lishid closed it with the concern that it complicates the sample plugin template. Thoughts @andymac4182 @woelfle and others?

[wonderbird]

Many thanks, @hjonasson