feat: refine unit test setup and add utils

[weboko]

Problem

Presently our setup can be more efficient and a lot of config duplications can be removed.

Solution

We should revisit our karma, chai setup.
Organize setup scripts for them and share between packages.

TODO

• move chai/mocha dependencies to root package.json;
• add root configuration for them with needed plugins such as chai-as-promised;
• unit tests have shared code that generates mocked objects for libp2p primitives - we need to decouple it to a new package @waku/test-utils (example of such utils - here);