Handle indexed sequence, and allow more backends for ConfigProvider

[afsalthaj]

Handling indexed sequence as given in the below example code, will allow more backends for ConfigProvider in zio-config.

The implementation is a simplified version of #7798, and it keeps backward compatibility.

object Hello extends App {

  val map =
    Map(
      "employees[0].age" -> "1",
      "employees[0].id" -> "1",
      "employees[1].age" -> "2",
      "employees[1].id" -> "2",
      "employees[2].id" -> "3",

    )

  val provider =
    ConfigProvider.fromMap(map)

  case class Employee(age: Option[Int], id: Int)

    val employee: Config[Employee] =
      Config.int("age").optional.zip(Config.int("id")).map(Employee.tupled)

  case class AppConfig(list1: List[Employee], dummyIds: List[Int])

  val config: Config[AppConfig] =
    Config.listOf("employees", employee).zip(Config.listOf("dummyIds.[0]", Config.int)).map(AppConfig.tupled)

  val pgm =
    provider.load(config)

  val result =
    Unsafe.unsafe(implicit u => zio.Runtime.default.unsafe.run(pgm.either).getOrThrowFiberFailure())

  assert(result == Right(AppConfig(List(Employee(Some(1),1), Employee(Some(2),2), Employee(None,3)),List(4, 6, 6))))

}

[adamgfraser]

Good to go when tests are passing!