Add release tools

[f1ames]

From what I see there is now ng build (and ng-build --prod) and also build-package script (which uses ng-packagr underneath).

I assume build-package was used previously to build package published to npm? So few thinks:

• Do we need ng build command itself or could we always use ng-packagr? Now it is a little confusing that we have two ways to build the package.
• What advantage ng-packagr gives as over using regular ng build?
• When it comes to npm publish we could use prepublishOnly package script same as in our React integration.

cc @engineering-this @jacekbogdanski

[engineering-this]

ng build is a command implemented by angular-cli. It builds the project with examples which are used for manual testing. Additionally calling ng test or ng e2e will in fact do ng build before running automated tests.

build-package uses only files from src/ckeditor to build the CKEditor component which is the only way to build package for publishing on NPM.

[engineering-this]

☝️ Actually README should be updated with above information.

[f1ames]

Ok, makes sense👌

So my proposal for solving this issue is to update the readme file as proposed in the above comment and package.json by adding prepublishOnly step which runs build-package script.

One more thing to check is ng build --prod. I am able to successfully run ng build and npm run build-package, but ng build --prod throws some errors:

[engineering-this]

Actually there is another issue. Both build-package and ng build outputs to same dist directory.

[engineering-this]

One more thing to check is ng build --prod. I am able to successfully run ng build and npm run build-package, but ng build --prod throws some errors:

It's some issue with webpack and terser-js, probably playing around with different versions of these would fix that issue, however it might bring new problems. I'd remove information about --prod flag from README, we don't need to build production version of samples as they are only for internal use.