ci: do not run release generation on forked repos by default

[Henrik66]

If RELEASE Github variable set, or manual github action, than run the job as before.

After https://github.com/dracutdevs/dracut/commit/9e1e924550a23b7fbbca5f752f32a749631db116 automatic releases are generated even on forked repos.

Use the same idea as in https://github.com/dracutdevs/dracut/commit/403f4e8e15da4fdc84f3d32a0f231eeb9b2e4ed0 to stop this from happening.

Also make version information optional as the script is now able to compute the version.