Update collect-assets to download kai assets from main branch / latest CI workflows

[sjd78]

Currently the collect-assets script only supports downloading kai binaries from released assets.

Two changes are needed.

First, to better support development cycles, the collect-assets scripts need to be able to download the kai assets from a workflow run on the more recent commit on the main branch of the kai repository.

• The kai build workflow runs with assets attached on the main branch: https://github.com/konveyor/kai/actions/workflows/build-and-push-binaries.yml?query=branch%3Amain+is%3Asuccess
• A recent run with the artifacts attached: https://github.com/konveyor/kai/actions/runs/12775086839

Second, the current kai build will also include some of the assets we currently static keep in the repo under assets/. What ever assets can be downloaded from the kai builds should be and the local copy removed.