Update signature handling and database connection management

- Changed `Signature` properties from `int` to `double` for precise positioning.
- Added necessary using directives in `EnvelopeReceiverController.cs` for database operations.
- Introduced a private `_cnnStr` field in `EnvelopeReceiverController` to store the connection string.
- Updated the constructor to accept `IOptions<ConnectionString>` for dependency injection of the connection string.
- Added a SQL command block to handle document element additions using a stored procedure.
- Configured the `ConnectionString` class in `Program.cs` to bind the connection string from app settings.
- Created a new `ConnectionString` class to manage the connection string value.

EnvelopeGenerator.Application/EnvelopeReceivers/Commands/Create/CreateEnvelopeReceiverDtos.cs

@@ -14,7 +14,7 @@ namespace EnvelopeGenerator.Application.EnvelopeReceivers.Commands.Create;
 /// <param name="X">X-Position</param>
 /// <param name="Y">Y-Position</param>
 /// <param name="Page">Seite, auf der sie sich befindet</param>
-public record Signature([Required] int X, [Required] int Y, [Required] int Page);
+public record Signature([Required] double X, [Required] double Y, [Required] int Page);
 
 /// <summary>
 /// DTO für Empfänger, die erstellt oder abgerufen werden sollen.