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

taskruns/clear-cache-taskrun.yaml

+apiVersion: tekton.dev/v1beta1
+kind: TaskRun
+metadata:
+  name: clear-cache
+spec:
+  taskRef:
+    name: clear-cache
+  params:
+    - name: drupalSiteName
+      value: test-dimitra-drupalsite
+  serviceAccountName: tektoncd