Create way to build rootfs images without using jenkins

As we are migrating to KernelCI v2 (API/Pipeline) and we are using same rootfs images, we need a way to build them conveniently, and upload to storage, preferable using web-interface.
Interface should provide following options:
* Select repository/branch
* Select name, specific architecture or all specified in config for this name, or build all possible images.
* Provide access to build logs
* Upload results automatically to storage

Start by reviewing the existing Jenkins-based rootfs image process and the KernelCI v2 API/Pipeline migration context. Define the web interface flow for repository and branch selection, image and architecture selection, build logs, and automatic storage upload. Done means these options are specified and the replacement workflow can build and publish the requested images without Jenkins.

Written by the indexing model from the issue text.