Finalize dependency specification DSL

[mkobit]

As of 0.7.x line, a few dependencies are specified with named fields on the extension:

sharedLibrary {
  coreVersion = "2.86"
  testHarnessVersion = "2.24"
}

There are also a few named dependencies in the inner dependencies declaration for plugins:

sharedLibrary {
  pluginDependencies {
    workflowCpsGlobalLibraryPluginVersion = "2.8"
  }
}

additional dependencies are added with the coordinates to the extension itself, which is similar to Gradle's dependency notation:

sharedLibrary {
  pluginDependencies {
    dependency("io.jenkins.blueocean", "blueocean-web", "1.2.4")
  }
}

These different methods can be confusing and should be aligned and fully documented for 1.0.0 release