Add Connection entity mapped to TBDD_CONNECTION table

Introduce a new `Connection` class in the `ReC.Domain.Entities` namespace.
The class is mapped to the `TBDD_CONNECTION` database table and includes
properties for various columns such as `Id`, `Bezeichnung`, `SqlProvider`,
and others. Attributes like `[Key]`, `[Column]`, and `[DatabaseGenerated]`
are used for database mapping. Nullable types are used for all properties.
Added necessary `using` directives for annotations and schema mapping.

src/ReC.Domain/Entities/Connection.cs

@@ -0,0 +1,53 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace ReC.Domain.Entities;
+
+[Table("TBDD_CONNECTION")]
+public class Connection
+{
+    [Key]
+    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
+    [Column("GUID")]
+    public short? Id { get; set; }
+
+    [Column("BEZEICHNUNG")]
+    public string? Bezeichnung { get; set; }
+
+    [Column("SQL_PROVIDER")]
+    public string? SqlProvider { get; set; }
+
+    [Column("SERVER")]
+    public string? Server { get; set; }
+
+    [Column("DATENBANK")]
+    public string? Datenbank { get; set; }
+
+    [Column("USERNAME")]
+    public string? Username { get; set; }
+
+    [Column("PASSWORD")]
+    public string? Password { get; set; }
+
+    [Column("BEMERKUNG")]
+    public string? Bemerkung { get; set; }
+
+    [Column("AKTIV")]
+    public bool? Aktiv { get; set; }
+
+    [Column("ERSTELLTWER")]
+    public string? ErstelltWer { get; set; }
+
+    [Column("ERSTELLTWANN")]
+    public DateTime? ErstelltWann { get; set; }
+
+    [Column("GEANDERTWER")]
+    public string? GeandertWer { get; set; }
+
+    [Column("GEAENDERTWANN")]
+    public DateTime? GeaendertWann { get; set; }
+
+    [Column("SYS_CONNECTION")]
+    public bool? SysConnection { get; set; }
+}