[MDEP-425] List plugin repositories

[wilx]

Fixes #868.

The list-repositories goal currently seeds dependency collection from the project's dependency repositories and reports repositories discovered in that dependency graph. Plugin repositories are available separately from the effective Maven project, so they never enter that collection and are omitted from the output.

This change reads the effective plugin repositories directly from MavenProject, then prints them in a distinct, mirror-aware section. The existing integration test now configures a plugin repository and verifies that both dependency and plugin repository sections are reported.

Validation:

• Confirmed the new integration-test assertions fail before the runtime change.
• mvn verify with Maven 3.9.16 and JDK 17.
• mvn -Prun-its verify with Maven 3.9.16 and JDK 17: 410 tests passed with one existing skip; all 99 Invoker builds passed.
• Focused list-repositories IT with Maven 4.0.0-rc-5 and JDK 17.

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