Refine docs on connecting to gitlab-toolbox in staging-ref environment

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The existing docs provide 2 example commands how how to connect to the gitlab-toolbox pod, both of which are actually slightly different in that one makes use of the -it option while the other doesn't.

However a user wanting to connect to the pod is only going to be interested in the specific command to start a bash shell so we can simplify this line of the docs to avoid situations where someone might misread the required command.

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Commits

• Refine docs on connecting to gitlab-toolbox in staging-ref environment

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