DevOps and Code Quality tasks

[priethor]

This is a collection of non-feature tasks that support the project in the realms of release management, code quality an continuous integration, etc.

Release Management

• Release management: automatically tag @since annotations with the correct version #151
• Release management: classify PRs in the right milestone to generate changelog #152
• Automatic changelog generation #153

Code quality

• PHP Stan Results #49
• Set up e2e testing environment #149
• Baseline E2E suite to cover primary flows #100
• Migration of old APIs and filenames to SCF namespace #150