Create `make_child_app()` function

[lauramaxwell]

Add a function that copies the relevant files from a parent app into a new child app. Key features are:

• [x] Copy app.R, R/app_ui.R and R/app_server.R and manifest.json from parent app to child app
• [x] Allow jobs folder to be copied from {matte} template or from parent app
• [ ] Option to include renv in the child app
• [x] Allow user to request app-as-package framework (golem or rhino) for child
• [x] Create dependencies in child app to include @import parent_app_name