New product features - default tasks, in-progress builds & more

This post introduces several new features and improvements for Bitbucket Cloud. For pull requests, it adds default tasks, a merge check for in-progress builds, the ability to change the destination branch directly, and refactors branch permissions and merge checks into a unified 'Branch Restrictions' feature. For Pipelines, it adds Docker BuildKit support with benefits like improved performance, secrets management, and caching, and launches an open beta for Linux shell runners that provide more flexibility by allowing direct access to host hardware. Bug fixes include improvements to workspace invitation deliverability and the UI for hiding repositories in a deleting state.