Receive `documentation` in `Config.links`

MR: Pending

Description

In this gitlab-web-ide-vscode-fork!88 (merged) we are now going to show the "Documentation" action in the Help menu. Right now the documentationUrl is hardcoded (1), but we want this to actually come from the config since a GitLab instance is responsible for providing it's own documentation links.

Acceptance Criteria

• An optional documentation is added to BaseConfigLinks
• Use this prop when we provide the documentationUrl to productConfiguration
• Default to https://docs.gitlab.com/ee/user/project/web_ide/