Automatically update submodules to latest #8425

Suggestion: we create automation script to automatically commit & push the latest submodules. (Edit 2020: via Github actions?)

Goals:

• prevent manual work in keeping submodules synchronised
• prevent build failures when new plugins were released and submodules not yet updated, (eg. https://github.com/piwik/piwik/commit/c4ca3c55f2892bee56c9e0bbda37530b3e1e4b7d was necessary to have green build)

Requires:

• git-lfs https://github.com/piwik/piwik/issues/7726
  • or alternatively, we do not automatically update the submodules tests/UI/expected-ui-screenshots since it doesn't work for this submodule to automatically keep it up to date

Can you think of any problem with automating sub-modules commit & push to latest?

from @diosmosis: let's investigate: http://stackoverflow.com/a/9189815 as it looks interestingly like it may be a core feature of git?