Basic empty Flink application for PageView

This MR is a first step towards a Flink "PageView" application that should read from webrequest_frontend_text and write into a new mediawiki.page_view topic.

The MR includes a commit in the git submodule that includes the new schemas, as they are needed to run tests.

None of those topics are streams yet, and this MR is just adding configs and data examples to work with them, but there is no logic yet.

This should help reviewing code, as smaller MRs should be easier to review than an MR with the whole application.

Next MR -> !147 (closed)

Bug: T425624