Docs: Add data source, interval, and ad hoc variable tasks (#26504)

* Create add-data-source-variable.md

* Update templates-and-variables.md

* Update menu.yaml

* Update add-interval-variable.md

* Update menu.yaml

* Update templates-and-variables.md

* Update add-interval-variable.md

* Update add-interval-variable.md

* ad hoc filters

* Update templates-and-variables.md

* Update templates-and-variables.md

* Update add-ad-hoc-filters.md

docs/sources/menu.yaml

@@ -261,6 +261,12 @@
       name: Add text box variable
     - link: /variables/add-constant-variable/
       name: Add constant variable
+    - link: /variables/add-data-source-variable/
+      name: Add data source variable
+    - link: /variables/add-interval-variable/
+      name: Add interval variable
+    - link: /variables/add-ad-hoc-filters/
+      name: Add ad hoc filters
     - name: Selection options
       link: /variables/variable-selection-options/
     - name: Value groups/tags