Disable gitlab_docs by default for Gitpod

What does this MR do and why?

In an effort to improve the bootup speed of Gitpod we're disabling gitlab_docs from being enabled by default. To enable gitlab_docs for a running instance going forward, simply run:

$ gdk config set gitlab_docs.enabled enabled
$ gdk reconfigure
$ gdk restart

Closes: #362457 (closed)

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