Add make_release_candidate.sh devtool

[charludo]

Motivation

We want to change our release process by including a staging branch. Commits should be moved to the staging branch in release candidates, and full releases consist of merging the state of the staging branch into main, as before.

A new dev tool should be created to help cherrypick commits, in order to make it easy to only include certain commits in a release candidate (for example: a hotfix should be included, a new feature unrelated to the previous release candidate should not).

Proposed Solution

Add a shell script which iterates over the commits made since the last full release, asking the user to y/n commits. Merge these commits into a new rc branch, and push to github.

Alternatives

Just add a wiki entry explaining the workflow.