Add capability to input different thickness values for web and flange for rectangular_hollow_section

[samuelbasimalla]

The current function definition of rectangular_hollow_section doesn't let different input values for thickness of flange and thickness of web. It is suggested to incorporate this as it is common in many projects to use custom hollow sections with different values for flange and web.

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Feature Request

[github-actions]

Thanks for opening your first issue in sectionproperties 🙌 Pull requests are always welcome 😉