set current git revision and git merge-base in ELN VERSION

[PiTrem]

set base revision and current revision in VERSION

The info from VERSION is displayed on the /about page of the ELN and should give the actual version tag and/or exact code revision and the closest ancestor from main or tag.

must have:

• base_revision: latest ancestor with main as obtained with git merge-base HEAD main
• current_revision : as obtained with git rev-parse HEAD

should have:

• correct version :

git describe --tags --exact-match `git rev-parse HEAD`

or

git describe --all --exact-match `git rev-parse HEAD`

could also have:

• base_tag : git describe --tags --abbrev=0 to show the closest tag ancestor

maybe:

• link to commit page on github?