Find a way to speed up UI image creation + build it always in CI/CD pipelines

UI is an integral part of DLE now. At the same time, we don't build UI image in CI/CD by default (job ui_build_ce_image_dev). This leads to confusion and mistakes when testing.

However, ui_build_ce_image_dev now lasts ~9 minutes (example). So we need to:

• first, find a way to speed it up significantly
• enable ui_build_ce_image_dev in CI/CD.
  • remove manual running
  • build image after merging into the master branch