Docs feedback: Clarify sentence in the 'High Availability (HA)' section of the 'Install GitLab' documentation

This sentence is unclear: To achieve this however is involved, It can be found in the documentation here.

Full paragraph: High Availability ensures every component in the GitLab setup can handle failures through various mechanisms. To achieve this however is involved, and the environments required can be sizable.

Text added by @grantyoung. 6c592007