[ATfL] Updated flows for Ubuntu packaging

Move the flows for Ubuntu packaging to a dedicated script.
This cleans up the GitHub Action to make it easier to add support for other operating systems in the future.

This patch uploads the tarball and the .deb package separately, allowing them to be downloaded independently from the GitHub Action.

Minor fix: rename the tarball to match the .deb file.

Author: vrukesh

.github/workflows/atfl_nightly_build_and_test.yml

@@ -23,6 +23,8 @@ jobs:
   build-and-test-toolchain:
     name: Build ${{ matrix.build_script }} for ${{ matrix.target_os }} on ${{ matrix.runner }}
     runs-on: ${{ matrix.runner }}
+    env:
+      ATFL_VERSION: "0.0"
 
     # Allow manual runs on Fork for testing, and
     # scheduled runs only on arm/arm-toolchain