Add a doctor command #1572

What happens

Diagnosing an environment problem means reading debug logs. The bug report template asks for the full DEBUG=testcontainers* output plus the OS, runtime, Node version and test runner, typed in by hand. There is no single place that shows what Testcontainers detected.

Expected

A command that prints a diagnosis that can be pasted into an issue:

npx testcontainers doctor

• the runtime strategy chosen, and why the others were rejected
• host, socket path, host IPs, runtime name and version
• which configuration is in effect, from environment variables and .testcontainers.properties
• whether registry credentials were found for the default registry
• whether Ryuk can be started and reached
• whether Docker Compose is available, and its version
• Node version and platform

The bug report template then asks for this output.

Where

• a new bin entry in packages/testcontainers/package.json
• .github/ISSUE_TEMPLATE/bug_report.md

Notes

• The package has no bin today.
• The same data could be exposed as a function for use in a test setup file.

Dependencies

• Blocked by Say why no container runtime was found #1571: it prints the per-strategy reasons that issue collects.
• Coordinate with Add programmatic configuration #1569: for reporting the effective configuration.