How we refactored the MySQL charms and created `mysql-shell-client` in the process

The MySQL charms are old. They have seen it all: started their life as Ensemble Formulas back in 2011 (which used to be a bunch of Bash scripts), evolved to Python functions decorated using the charms.reactive library, and became one of the first family of charms rewritten with the ops Python framework in 2019. Since their last rebirth, our Data Platform team has matured, and our shared understanding of the best practices on how to develop resilient Charms for Juju has evolved significantly. In...