IGNITE-23703 .NET: Add client pool

[ptupitsyn]

Add IgniteClientPool to simplify DI integration.

IgniteClient.StartAsync is asynchronous and can't be easily used in DI containers, which typically require a synchronous factory method. Also, multiple client instances might be required for high load scenarios.

Usage example:

// Register in DI container
builder.Services.AddSingleton<IgniteClientPool>(_ => new IgniteClientPool(
        new IgniteClientPoolConfiguration
        {
            Size = 3,
            ClientConfiguration = new("localhost"),
        }));

...

// Invoke in a controller
public async Task<IActionResult> Index([FromServices] IgniteClientPool ignite)
{
    var client = await ignite.GetClientAsync();
    var tables = await client.Tables.GetTablesAsync();
    return Ok(tables);
}

[gurustron]

Maybe move the following:

builder.Services.AddSingleton<IgniteClientPool>(_ => new IgniteClientPool(

Into a specific AddIgniteClientPool method accepting setup action.

[gurustron]

not thread safe =)))

[gurustron]

Maybe follow the factory pattern - as EF Core does with IDbContextFactory? Pool without returning to the pool is a bit confusing TBH.