GitHub action to test UI before merging code

[upkarlidder]

Adding GitHub action to install, build and test the UI component on every

• commit to any branch
• PR to the main branch

The action does the following

• for all configurations in the matrix (currently just Node.js 14)
• install dependencies - making sure package.json file is valid and there are no major security issues from npm
• cache dependencies for next run
• build the production site
• run unit tests
• run yarn lint

If all of the above passes, new code can be merged in.

Sample run - https://github.com/Call-for-Code-for-Racial-Justice/Five-Fifths-Voter/runs/3682040517?check_suite_focus=true

Related to #232

@davidnixon @GeraldMit: pls review and merge. I also had to comment out the default test that comes with vue.js. It fails as we don't have the helloworld component in this project. We need to create more relevant tests. Captured in #136. Need another issue for general unit testing.

FYI @demilolu

[GeraldMit]

approved but had an issue, need to setup to run on a new machine so unable to validate at the moment for pull req.