docs: added a page for default select menu values. Added a section in components3 for role select menus

[Jaskowicz1]

This PR adds a new page for default values in a select menu, added by #889 (meaning this PR can not merge til that PR merges). This PR also adds a section in components3.md for role select menus, showing people how to create other select menus that aren't just text based.

Documentation change checklist

• My documentation changes follow the same style as the rest of the documentation and any examples follow the coding style guide.
• I tested that my change works before raising the PR (via running doxygen, and testing examples).
• I have not moved any existing pages or changed any existing URLs without strong justification as to why.
• I have not generated content using AI or a desktop utility such as grammarly.

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[Jaskowicz1]

Re-running Test Compile action before merge.