Show deploy command not only for projects

[akerekes]

Currently the Deploy to App Engine Standard... context menu item is only shown if the user clicks on the project. We could make this a bit more flexible by showing the item on other items as well, i.e. elements that specify locations for appengine-web.xml/app.yml that can be passed to the deploy process (or these xml/yml files themselves)

[briandealwis]

Partial motivation from @chanseokoh:

I have seen people having multiple GCP modules (or services?) in a single project, mixing Python and Java, but I don't think we will support that kind of setup anytime soon.

We could at least support Deploy for these contained projects.

[akerekes]

We can also support multiselect, and pass to gcloud deploy all of the selected applications in one go.