chore(gatsby): Add yarn shortcuts for running tests with devtools

[pvdz]

Adds two yarn/npm run aliases;

• yarn jest:inspect will run jest through node --inspect
• yarn jest:inspect-brk will run jest through node --inspect-brk

The difference is that one (--inspect-brk) will wait for the devtools to connect and pause at the start. This one requires you to explicitly press the start button before the code starts running (once hooked up). The other one (--inspect) will start running immediately after connecting to devtools.

(For anyone looking at this; The way you use this is to go to chrome/chromium and open the pseudo-url about:inspect. In there click the "open dedicated window for node" link (see screencap). Once that window is open, node --inspect and node --inspect-brk will automatically start debug sessions in that devtools popup. To debug a Gatsby test you would run yarn jest:inspect some/feat.js -t "test case". )

[wardpeet]

LGTM

[muescha]

i would like to see the small "qickstart" also somewhere in the docs...

[muescha]

ah - found it here with examples for gatsby build - not for tests:
https://www.gatsbyjs.org/docs/debugging-the-build-process/#chrome-devtools-for-node