[Backport 2.19] Guard eclipse() to spotless tasks and keep P2 mirror on pinned version (security)

[opensearch-ci-bot]

Backport e81ceeb from #6461.

[DarshitChanpura]

Change is not compatible with current CI:

A problem occurred configuring root project 'opensearch-security'.
> Could not resolve all artifacts for configuration 'classpath'.
   > Could not resolve com.diffplug.spotless:spotless-plugin-gradle:8.10.1.
     Required by:
         root project : > com.diffplug.spotless:com.diffplug.spotless.gradle.plugin:8.10.1
      > Dependency requires at least JVM runtime version 17. This build uses a Java 11 JVM.

[cwperks]

@peterzhuamazon failing with the following

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'opensearch-security'.
> Could not resolve all artifacts for configuration 'classpath'.
   > Could not resolve com.diffplug.spotless:spotless-plugin-gradle:8.10.1.
     Required by:
         root project : > com.diffplug.spotless:com.diffplug.spotless.gradle.plugin:8.10.1
      > Dependency requires at least JVM runtime version 17. This build uses a Java 11 JVM.

failures need to be resolved