In order to be able to externalize pipelines or user-defined operators better, we want to add an apply <script> operator. <script> may either be an absolute path to a .tql file, or just an identifier that is autocompleted to <script-dir>/<identifier>.tql, where <script-dir> is a directory inside the config directory.
### Definition of Done
- [x] Implement and document the `apply` operator
In order to be able to externalize pipelines or user-defined operators better, we want to add an
apply <script>operator.<script>may either be an absolute path to a.tqlfile, or just an identifier that is autocompleted to<script-dir>/<identifier>.tql, where<script-dir>is a directory inside the config directory.