Split your pipelines workflows across multiple files

Introduces the ability to split Bitbucket Pipelines definitions into multiple YAML files within a repository, improving modularity, reusability, and maintainability of CI/CD configurations. This feature allows for defining pipelines in separate files (e.g., `.bitbucket/shared-pipelines.yml`) and importing them into the main `bitbucket-pipelines.yml` file. It also enables exporting shared pipelines for use across different repositories within the same workspace.