Add button for new case contact

[MikeRose151]

What github issue is this PR for, if any?

Resolves #6501

What changed, and why?

Added a + new case contact button to the new design of the case contacts table. This button takes the user to the already-existing "new case contact" form.

How is this tested? (please write rspec and jest tests!) 💖💪

to be added

Note: if you see a flake in your test build in github actions, please post in slack #casa "Flaky test: " :) 💪 Note: We love capybara tests! If you are writing both haml/js and ruby, please try to test your work with tests at every level including system tests like https://github.com/rubyforgood/casa/tree/main/spec/system

Screenshots please :)

Run your local server and take a screenshot of your work! Try to include the URL of the page as well as the contents of the page.

[compwron]

Very cool! Please add a test and then we can merge :)

[compwron]

How's it going?