This installs the eslint and @beanbag/eslint-plugin dependencies

when setting up the Djblets package, along with a .eslintrc.yaml.
This will aid in ensuring our JavaScript and TypeScript code meets our

guidelines, especially with editor support enabled.
Right now, much of Djblets does not pass our lint checks. This will be

addressed separately.

Set up Djblets in development mode and verified that I could run

ESLint with our plugin and settings. Checked by manually running

ESLint and checking in my editor.