feat(Tabs): clarify when to use button groups instead of tabs

What does this MR do?

Tabs have been commonly used in a variety of pages to off a mechanism to switch between content. However, applying tabs to all scenarios is not the best choice.

Here are a few examples of places where tabs are best served due to differentiated content

Merge requests	Pipelines

Here are a few examples of places where tabs could be replaced by a button group instead.

Tab Group	Button Group

This merge request updates documentation for button and tab components. For buttons, it clarifies the use using GlButtonGroup instead of the deprecated segmented control, and updates information about pagination. For tabs, it adds guidance on when to use button groups instead of tabs for toggling between a small set of related options.

Does this MR meet the acceptance criteria?

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• The “What does this MR do?” section in the MR description is filled out, explaining the reasons for and scope of the proposed changes, per “Say why not just what”.
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