feat: remove minimal version requirement in favour of per-feature checking
This MR removes the hard requirement for the GitLab version introduced in !252 (merged). Instead, we throw a new UnsupportedVersionError
every time the user tries to make a request that is not supported by their GitLab instance:
- working with MR discussions - supported in 13.5+
- CI config file validation - supported in 13.6+
Related to #428 (closed)
Edited by Tomas Vik