Make installing development NPM package by commit simpler

[bahmutov]

We can install and test development versions of cypress using TGZ npm package and custom binary path, but it is a huge hustle.

CYPRESS_BINARY_PATH=https://cdn.cypress.io/beta/binary/3.1.0/mac64/buildkite-develop-4ead424d4c9e3d65422c71597496539290720057-32310/cypress.zip npm i https://cdn.cypress.io/beta/npm/3.1.0/circle-develop-4ead424d4c9e3d65422c71597496539290720057-32306/cypress.tgz

It would be so much simpler if we could install NPM package and binary by using just a single TGZ url with commit SHA or at least branch name plus SHA

Something like: npm i -D https://on.cypress.io/beta/develop/4ead424d4c9e3d65422c71597496539290720057 where develop is branch name followed by SHA

The redirect service redirect to cypress.tgz stored on cdn.cypress.io/beta/npm/... then our NPM package would be smart to look at the original installation URL before looking at CYPRESS_BINARY etc

I did an experiment and NPM gives the original installation URL / path as an environment variable to the post install script, see https://github.com/bahmutov/test-npm-install-from-tgz. Thus the NPM package could determine its branch and SHA by inspecting npm_config_argv object, then download the right binary (we have to update on.cypress.io to make this more convenient)

This will make testing development version of test runner so so simple

[jennifer-shehane]

Closing in favor of #4525