Simplify the version variable in the build CI workflow

[Thykof]

Sometime the version of Massa Station must be prefixed by "v" (v4.0.1), sometime not. It's the mess in the CI and the installer script.

• the version passed to the create release job must contain a v prefix (v4.0.1)
• the version API endpoint returns the v prefix (v4.0.1), the front display it without modification.
• the script create_pkg.sh remove the v prefix
• the script create_deb.sh remove the v prefix
• the script build_installer.pyfor windows remove the v prefix from the version variable
• the job build-packages-windows remove the v prefix in the Sign Windows binary step
• the job build-macos-installer remove the v prefix in all cases

this means that the job build-packages-windows, build-deb-installer and build-macos-installer don't want the v prefix.

we could

• remove the v prefix before forwarding the version variable in the build install job
• remove the code that remove the v prefix in the installer scripts
• add the v prefix in the endpoint