Docs feedback: Indicates the LSIF versions supported by Gitlab Code Intelligence

Related doc: https://docs.gitlab.com/ee/user/project/code_intelligence.html

Code Intelligence is a wonderful feature. However, currently the document about code intelligence doesn't mention the LSIF version supported by GitLab. In the meantime, the version of LSIF is evolving quickly. I think it's important for GitLab to mention which versions of LSIF are supported so users can choose or develop the right tool to generate the LSIF file that GitLab can understand.