Introducing Package triggers in Bitbucket Pipelines

Introduces a new `package-artifact-created` trigger for Bitbucket Pipelines. This trigger allows custom pipelines to be automatically run when a package artifact is created in Bitbucket Packages. It enables automation of post-publish workflows like validation, scanning, promotion, and notifications. The trigger provides package-specific variables (`BITBUCKET_TRIGGER_PACKAGES_PACKAGE_TYPE`, `BITBUCKET_TRIGGER_PACKAGES_PACKAGE_NAME`, `BITBUCKET_TRIGGER_PACKAGES_ARTIFACT_NAME`) for use in conditions and scripts. The post also details limitations on trigger conditions, pipeline initiation, and preventing infinite loops with other trigger types.