Gitlab CI generator should gzip files

Problem to solve

Gitlab doesn't Gzip pages files by default, you have to do it.

Who will benefit

People reading the docs

Proposal

Add a gzip line to the generate CI thing:

https://gitlab.com/gitbuilding/gitbuilding-example/-/blob/dbad3a5f07f4b3396e1ba8b49d4980586ccb60aa/.gitlab-ci.yml#L14-15