[precompiled]: rebuild/overwrite the image even if the tag already exists

[shivakunv]

Add FORCE_PUSH override to overwrite already-published precompiled images

Issue: When a CVE is found during a release and the precompiled image is already published, the pipelines skip re-pushing because the image tag already exists. If no new kernel has been released, there is no way to rebuild and overwrite the fixed image

Solution: Write the existing FORCE_PUSH into both scheduled pipelines(github and gitlab) so it can be toggled via a CI/CD variable.
Setting FORCE_PUSH=true forces a rebuild, e2e test, and overwrite of the existing tag.
Unset keeps the normal skip.

[shivakunv]

not planned, as ubuntu26.04 is released with vex exception