P2 mirror for maven plugin

[jibidus]

Support configuration of P2 mirrors in maven plugin (fixes #1697).

Here is how to declare new mirrors:

  <eclipse>
   …
    <p2Mirrors>
      <p2Mirror>
        <prefix>https://download.eclipse.org/</prefix>
        <url>https://some.internal.mirror/eclipse</url>
      </p2Mirror>
    </p2Mirrors>
  </eclipse>

Notes:

• I tried to write a test with Wiremock, but didn't succeed 😢 (cannot find how to declare a trusted certificate, since connection is through SSL)
• I cannot test manually by publishing a new version locally 😢 (./gradlew publishToMavenLocal fail with error Configuration cache problems found in this build)

[nedtwigg]

Shipped in plugin-gradle 6.22.0 and plugin-maven 2.40.0.

[jibidus]

Thanks !