Add programmatic configuration #1569

What happens

Configuration comes only from environment variables and .testcontainers.properties, and each setting is read where it is used. Fourteen variables are read through process.env across packages/testcontainers/src (Ryuk image, port, privileged, verbose and disabled flags, the SSHD image and port, the hub image prefix, reuse, Docker auth config and others), plus the Docker host settings in the strategy config.

• Changing a setting from code means assigning to process.env before the first container starts.
• Nothing is typed or validated. A misspelt variable is silently ignored.
• There is no way to read the effective configuration.

Expected

A typed configuration object with one place that resolves it:

TestContainers.configure({
  ryuk: { disabled: false, privileged: true },
  hubImageNamePrefix: "registry.example.com/mirror",
  reuse: { enabled: true },
});

• Environment variables and the properties file keep working, with a documented precedence.
• TestContainers.getConfiguration() returns what is in effect.

Where

• packages/testcontainers/src/container-runtime/strategies/utils/config.ts
• the process.env reads in reaper/reaper.ts, port-forwarder/port-forwarder.ts, container-runtime/image-name.ts, generic-container/generic-container.ts and container-runtime/auth/
• packages/testcontainers/src/test-containers.ts

Notes

• Java centralises this in TestcontainersConfiguration.
• Configuration must be set before the runtime client and Ryuk are created. Decide what happens when it is changed afterwards.

Dependencies

• Nothing blocks this. It can start now.
• Coordinate with Make the logger replaceable #1568: the logger is a natural configuration setting.