web: Get rid of remaining eslint warning

.. by defining the Interaction interface (translated from
scap/spiderpig/model.py) and using it as the type of the
interaction prop of the SpInteraction component. Thanks to Eric
Gardner for assistance!

Since this added the first TypeScript file to the project, I had to
tweak .eslintrc.json to add TypeScript support and update the
package list in package.json accordingly.

Add npm run test to the Gitlab CI pipeline