Docs: Use https scheme for Grafana playground links (#21360)

docs/sources/features/datasources/elasticsearch.md

@@ -168,7 +168,7 @@ In the above example, we have a lucene query that filters documents based on the
 a variable in the *Terms* group by field input box. This allows you to use a variable to quickly change how the data is grouped.
 
 Example dashboard:
-[Elasticsearch Templated Dashboard](http://play.grafana.org/dashboard/db/elasticsearch-templated)
+[Elasticsearch Templated Dashboard](https://play.grafana.org/dashboard/db/elasticsearch-templated)
 
 ## Annotations
 

docs/sources/features/datasources/graphite.md

@@ -147,7 +147,7 @@ Why two ways? The first syntax is easier to read and write but does not allow yo
 the second syntax in expressions like  `my.server[[serverNumber]].count`.
 
 Example:
-[Graphite Templated Dashboard](http://play.grafana.org/dashboard/db/graphite-templated-nested)
+[Graphite Templated Dashboard](https://play.grafana.org/dashboard/db/graphite-templated-nested)
 
 ### Variable Usage in Tag Queries
 

docs/sources/features/panels/table_panel.md

@@ -17,7 +17,7 @@ weight = 4
 The table panel is very flexible, supporting both multiple modes for time series as well as for
 table, annotation and raw JSON data. It also provides date formatting and value formatting and coloring options.
 
-To view table panels in action and test different configurations with sample data, check out the [Table Panel Showcase in the Grafana Playground](http://play.grafana.org/dashboard/db/table-panel-showcase).
+To view table panels in action and test different configurations with sample data, check out the [Table Panel Showcase in the Grafana Playground](https://play.grafana.org/dashboard/db/table-panel-showcase).
 
 ## Querying Data