LPS-47374 Content Targeting as an app in plugins SDK

Hey Brian,

As discussed, the Content Targeting project will be a submodule under plugins/apps. I send you the required changes.

The commit brianchandotcom/liferay-portal/pull/19021 adds the submodule to master, this time under portal/modules/apps, but it hasn't been merged yet.

Thanks!

@juliocamarero