Switch to prettier formatting in juggler monorepo

[bajtos]

This story requires the new monorepo to be created first, see #1725.

Configure automatic formatting of source code using Prettier. The solution should pretty much copy what we have in loopback-next.

Acceptance criteria

The changes should be split to (at least) the following two commits:

Setup Prettier infrastructure

• Add .prettierrc from loopback-next
• Add a new script npm run lint to check whether all source code is formatted according to Prettier rules. This script should be run from posttest script too.
• Add a new script npm run lint:fix to automatically fix linting errors.
• Add a CI step to run npm lint, see how loopback-next does it.

Reformat the code

• Execute npm run lint:fix to reformat the code.

[stale]

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[stale]

This issue has been closed due to continued inactivity. Thank you for your understanding. If you believe this to be in error, please contact one of the code owners, listed in the CODEOWNERS file at the top-level of this repository.