Make 8.x-1.x the default branch

Problem/Motivation

Currently, 7.x-1.x is still set as the default branch. This can be confusing for developers when working on an issue or manually cloning the repository. Furthermore, merge requests will always default to the default branch no matter the version set in the issue.

Steps to reproduce

Proposed resolution

Make 8.x-1.x the default branch

Remaining tasks

User interface changes

API changes

Data model changes