Draft: ci: generate dev versions with next version number of commits since previous version

The generated dev versions look like the ones of the nightly builds of numpy 1, matplotlib or pandas: 24.0.dev28+g1d4ef94d where the main version 24.0 is defined in the version_next.text file, 28 (in dev28) is the number of commits since the previous tag and 1d4ef94d is the commit hash.

Unfortunately, it is not possible to create GitLab CI variables with the correct values of the versions. As a consequence, this commit adds the CI job calculate_versions that calculates the versions and write them into a file. CI jobs that require versions can read them from this file.