Improve storefront build performance by adding SASS Embedded

This change enables SASS Embedded for the storefront build process. The webpack compile time decreased from 2408 ms to 559 ms, which is approximately a 77 percent improvement. This makes the storefront build more than four times faster. With SASS Embedded installed: ``` shopware-6-storefront (webpack 5.97.1) compiled with 26 warnings in 559 ms ``` Without: ``` shopware-6-storefront (webpack 5.97.1) compiled with 26 warnings in 2408 ms ```