[Enhancement] GitLab document

I have few suggestions to add over gitlab side from our internal confluence page. Confluence pages:

1. GitLab CI with Maven: https://www.ebi.ac.uk/seqdb/confluence/display/EXT/GitLab+CI+with+Maven
2. GitLab EE: https://www.ebi.ac.uk/seqdb/confluence/display/EXT/Gitlab+EE+%2C+Web+Production+Instance
3. Gitlab Usage: https://www.ebi.ac.uk/seqdb/confluence/display/EXT/Gitlab+Usage

Please review them.