enh(NcAppNavigationItem): Allow to pass SVG or path as icon property

[susnux]

☑️ Resolves

Not only allow icon classes (somewhat deprecated) but also SVG or SVG paths as icon property.

🖼️ Screenshots

🏁 Checklist

• [x] ⛑️ Tests are included or are not applicable
• [x] 📘 Component documentation has been extended, updated or is not applicable

[ShGKme]

Is it required for a specific place? Why not use the icon slot?

[susnux]

Why not use the icon slot?

I can do so. Whats then the plan with the icon props? Should we deprecate them as icon classes are deprecated and just recommend using icon slots with svg wrapper. Or should be move them to SVG support?