Overarching issue to track development of a script to apply upgrade macros in LFRic Apps and Core. Development of this script has taken place in LFRic Apps Ticket #139, but during development there, it was decided that the script would be more suited to living here, as some parts may be used as libraries in tools applicable across multiple repos.

The code has been ported to github from trac in this branch. However, as the script is entirely new and quite large, to aid reviewers there will be 2 PRs:

• One to add the code that reads versions.py files, combines macros and rewrites the files. This is the majority of the code added.
• One to add the code to run rose app-upgrade commands and to add the unit tests.