Make automated action that creates a PR to develop if a PR is merged directly into master

[LuisDuarte1]

In this way we can adopt the fix workflow that we discussed in the past Thursday meeting:

1. Make fix on the master branch
2. Make a PR into the master branch
3. Upon merging, the action will automatically create a PR to merge this changes into develop
4. If necessary, do some fixes to work in the develop branch
5. Upon approval, merge into develop

I think this is the most streamlined and error-free approach into getting fixes done in master but also in develop.
Maybe this should be a seperate action workflow, and maybe done on a seperate issue, that listens to merged pull request events into `master, wdyt?

Originally posted by @LuisDuarte1 in #930 (comment)

[bartekpacia]

When migrating to Fastlane, we could use this plugin I made:

https://github.com/bartekpacia/fastlane-plugin-get_new_build_number