Allow `@Nested` class lifecycle to be configured via `junit.jupiter.testinstance.lifecycle.default`

[nlisker]

Related to #1575.

The configuration junit.jupiter.testinstance.lifecycle.default applies only to top level classes (by my tests - I didn't see it documented). I would have expected it to work for nested classes as well.

Deliverables

• An option to globally configure the lifecycle of nested classes
• Preserve backwards compatibility (the current behavior)

[nlisker]

Looks like the issue comes from an extension, not JUnit directly.

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