Add tasks

• Added Task and its TaskRun for cleaning cache of a Drupal site.
• Added Task and its TaskRun for database backup of a Drupal site.
• Added Task and its TaskRun for database restore of a Drupal site.
• Added Task and its Taskrun for editing DrupalSite.spec.publish.

Relates to https://gitlab.cern.ch/webservices/webframeworks-planning/-/issues/297

README.md

+# Drupal operations
+
+This project includes operations on Drupal sites or across infrastructure that are not part of the drupalSite-operator, such as Tekton tasks.
+
+We implement actions that the infrastructure users can apply ad-hoc to their websites, and also other infrastructure components can use to perform their tasks.