Fix dapper example

[molostovvs]

Parameters with the $ prefix are currently not supported, so we need to fix the example.

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

At the moment the example for dapper uses parameters with the prefix $, which is currently unsupported and causes an error when executing the request.

What is the new behavior?

The corrected example uses the @ prefix for parameters, which is supported by sdk.

Other information

At the moment (sdk 0.7.0) a simple query made using an example like:

await connection.ExecuteAsync(
    "insert into items (addtime, name) values (@AddTime, @ItemName)",
    new { AddTime = DateTime.UtcNow, ItemName = item });

results in an error:

{"errorMessage":"Status: GenericError, Issues:\n[0] (:1:43)Error: Unknown name: $AddTime\n","errorType":"YdbException","stackTrace":"   at Ydb.Sdk.Ado.YdbDataReader.NextExecPart()\n   at Ydb.Sdk.Ado.YdbDataReader.Init()\n   at Ydb.Sdk.Ado.YdbDataReader.CreateYdbDataReader(IAsyncEnumerator\u00601 resultSetStream, Action\u00601 onStatus, YdbTransaction ydbTransaction)\n   at Ydb.Sdk.Ado.YdbCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)\n   at Ydb.Sdk.Ado.YdbCommand.ExecuteReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)\n   at Ydb.Sdk.Ado.YdbCommand.ExecuteNonQueryAsync(CancellationToken cancellationToken)\n   at Dapper.SqlMapper.ExecuteImplAsync(IDbConnection cnn, CommandDefinition command, Object param) in /_/Dapper/SqlMapper.Async.cs:line 662\n   at Bot.Commands.AddCommand.ExecuteAsync(ITelegramBotClient bot, Int64 chatId, DbConnection connection) in /home/mvs/source/playground/tg-bot/src/Bot/Commands/AddCommand.cs:line 15\n   at Bot.Handler.FunctionHandler(Request request) in /home/mvs/source/playground/tg-bot/src/Bot/Handler.cs:line 53\n   at CallSite.Target(Closure, CallSite, Object)\n   at Yandex.Cloud.Runtime.DefaultRuntime.Start() in /bootstrap/runtime/DefaultRuntime.cs:line 57\ninner:\n"}

[KirillKurdyukov]

You're right. The example won't work for the latest version, but it's not about the parameter.