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.GeneratorAPI/Program.cs

@@ -90,6 +90,9 @@ builder.Services.AddSwaggerGen(options =>
 builder.Services.AddOpenApi();
 // DbContext
 var connStr = config.GetConnectionString("Default") ?? throw new InvalidOperationException("There is no default connection string in appsettings.json.");
+
+builder.Services.Configure<ConnectionString>(cs => cs.Value = connStr);
+
 builder.Services.AddDbContext<EGDbContext>(options => options.UseSqlServer(connStr));
 
 builder.Services.AddAuthHubClient(config.GetSection("AuthClientParams"));