test: Implemented initial tests for plugin

[GuiLeme]

What does this PR do?

It implements a series of tests for pick-random-user. The strategy used is pretty simple, we'll use 3 different types of tests (for now):

• Structural tests (To make sure everything is rendered in the correct place);
• Behavioral tests:
  • For one user - Test if the plugin works as expected for moderator alone;
  • For multiple users (In this first case - 1 moderator and 1 attendee) - to really test some of the main functionalities like pick user, re-pick user, etc.

Those 3 types of tests will be done in a single meeting session each (and because of that 3 different workers each).

Motivation

2 main reasons we're implementing end-to-end testing:

• keep behavior after dependency update (npm audit fix --force, for example);
• keep behavior after refactor;

More

There are plenty of documentation to execute the tests in the tests readme, so I invite the reviewer and any other interested party to take a look and provide feedback, if needed.