Change version format (snapshots and main branch)

[geyslan]

Description

For snapshot releases and main branch builds version should be

main-d83c07b5b

instead of

v0.21.0-rc-103-gd83c07b5b

The latter doesn't communicate precisely, since even after the official release, it still uses the release candidate tag as its ancestor (due to the release tag pointing to the release branch, not to main).

[geyslan]

This might be solved automatically by changing the release approach (still in analysis). Let's see. @rscampos @itaysk