WebAPI for database integrity added

Restructure the solution
* The project has been split into the database integration "src/webapi" and the Blazor wasm project "src/y4f".

WebAPI
* API with CRUD capabilities

* The main task of the "WebAPI" project is to access the database data and make it available to the Blazor-WASM project via an API.

* GET example of the allergy table via the file "TestFetchAllergienData.razor", which can be tested via the browser "/TestFetchAllergienData".

src/WebApi/Models/Allergie.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Allergie
+{
+    public int Idallergie { get; set; }
+
+    public string? Beschreibung { get; set; }
+
+    public virtual ICollection<Menuitem> MenuItemIdmenuItems { get; set; } = new List<Menuitem>();
+}

src/WebApi/Models/Bestellungsposition.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models; 
+
+public partial class Bestellungsposition
+{
+    public int Idbestellung { get; set; }
+
+    public int? Menge { get; set; }
+
+    public DateTime? Datum { get; set; }
+
+    public int KundeIdkunde { get; set; }
+
+    public int RabattIdrabatt { get; set; }
+
+    public virtual Kunde KundeIdkundeNavigation { get; set; } = null!;
+
+    public virtual Rabatt RabattIdrabattNavigation { get; set; } = null!;
+
+    public virtual ICollection<Menuitem> MenuItemIdmenuItems { get; set; } = new List<Menuitem>();
+}

src/WebApi/Models/Kunde.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Kunde
+{
+    public int Idkunde { get; set; }
+
+    public string? Code { get; set; }
+
+    public int? Treuepunkte { get; set; }
+
+    public virtual ICollection<Bestellungsposition> Bestellungspositions { get; set; } = new List<Bestellungsposition>();
+}

src/WebApi/Models/Menuitem.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Menuitem
+{
+    public int IdmenuItem { get; set; }
+
+    public string? Bezeichnung { get; set; }
+
+    public string? Zusatzinformation { get; set; }
+
+    public decimal? Preis { get; set; }
+
+    public int MenuItemKategorieIdmenuItemKategorie { get; set; }
+
+    public virtual Menuitemkategorie MenuItemKategorieIdmenuItemKategorieNavigation { get; set; } = null!;
+
+    public virtual ICollection<Allergie> AllergieIdallergies { get; set; } = new List<Allergie>();
+
+    public virtual ICollection<Bestellungsposition> BestellungspositionIdbestellungs { get; set; } = new List<Bestellungsposition>();
+}

src/WebApi/Models/Menuitemkategorie.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Menuitemkategorie
+{
+    public int IdmenuItemKategorie { get; set; }
+
+    public string? Bezeichnung { get; set; }
+
+    public int MenuItemUeberkategorieIdmenuItemUeberkategorie { get; set; }
+
+    public virtual Menuitemueberkategorie MenuItemUeberkategorieIdmenuItemUeberkategorieNavigation { get; set; } = null!;
+
+    public virtual ICollection<Menuitem> Menuitems { get; set; } = new List<Menuitem>();
+}

src/WebApi/Models/Menuitemueberkategorie.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Menuitemueberkategorie
+{
+    public int IdmenuItemUeberkategorie { get; set; }
+
+    public string? Bezeichnung { get; set; }
+
+    public virtual ICollection<Menuitemkategorie> Menuitemkategories { get; set; } = new List<Menuitemkategorie>();
+}

src/WebApi/Models/Rabatt.cs

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+using System;
+using System.Collections.Generic;
+
+namespace WebApi.Models;
+
+public partial class Rabatt
+{
+    public int Idrabatt { get; set; }
+
+    public decimal? Prozent { get; set; }
+
+    public DateTime? GueltigkeitVon { get; set; }
+
+    public DateTime? GueltigkeitBis { get; set; }
+
+    public virtual ICollection<Bestellungsposition> Bestellungspositions { get; set; } = new List<Bestellungsposition>();
+}