`input-group-text` larger than normal font size

Upon investigating https://gitlab.com/gitlab-org/gitlab-ce/issues/59189, we noticed that the input-group-text which contains the hostname in front of the namespace selector, has larger text than the rest of the UI.

This is due to a font-size: 1rem rule that's ultimately rendering the text at 16px, instead of the standard 14px.

Given input-group-text is used in multiple places, we need to figure out how to correct this without disrupting other usages of this.