Create E2E tests with `cypress` or `puppeteer` against dev docs, and run it before each commit.

[JustFly1984]

Currently we have no tests implemented at all. We have Typescript, Eslint, docs generation and gatsby.js example

We can't use dom based tests with node.js environment, cos we need to have window.google global object created by google-maps-api script, loaded in runtime by <LoadScript /> component.

We need to run headless browser tests with cypress against dev docs build before each commit with husky and lint-staged

[JustFly1984]

There is a gatsby-plugin-cypress, which we can leverage for testing gatsby-example

[JustFly1984]

We could use puppeteer https://www.youtube.com/watch?v=MbnATLCuKI4