OZG-7707 Add icons showcase to demo app

alfa-client/apps/demo/project.json

alfa-client/apps/demo/src/app/app.component.html

alfa-client/apps/demo/src/app/app.component.ts

alfa-client/apps/demo/src/app/app.config.ts

alfa-client/libs/design-system/src/assets/accessibility.svg

alfa-client/libs/design-system/src/assets/account-circle.svg

alfa-client/libs/design-system/src/index.ts

...nt/libs/design-system/src/lib/icon/icon.component.spec.ts

...-client/libs/design-system/src/lib/icon/icon.component.ts

alfa-client/libs/design-system/src/lib/icon/icon.stories.ts

alfa-client/package.json

alfa-client/pnpm-lock.yaml