fix(products): menu item selection in product manager

[marfavi]

This PR resolves #47.

Now can correctly display and select menu items in the product management page.

This is done by implementing equality members on MenuItem

[A-Guldborg]

Is this the right approach, to change to a class? @TTA777 is more knowledgeable on C# practices so I don't know, but there are a few things that confuses me:

The component that displays the menu items is the MudComboBox which in their own example for "Complex Type" (see code under the Chip Customization example) does not override IEquatable.

Likewise, C# documentation for record value equality shows that two records are equal if their values are equal. How does this change then change the equality functionality for our menu items? 😅

[marfavi]

How does this change then change the equality functionality for our menu items? 😅

Good question. The only answer I can give is that this fixes the issue.

Using other components (like MudSelect or MudSelectExtended) still won't work without this fix.