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

docs/sources/guides/whats-new-in-v2-5.md

@@ -37,7 +37,7 @@ and complex queries for logs or metrics.
 - Query only relevant indices based on time pattern
 - Alias patterns for short readable series names
 
-Try the new Elasticsearch query editor on the [play.grafana.org](http://play.grafana.org/dashboard/db/elasticsearch-metrics) site.
+Try the new Elasticsearch query editor on the [play.grafana.org](https://play.grafana.org/dashboard/db/elasticsearch-metrics) site.
 
 ### CloudWatch
 

docs/sources/guides/whats-new-in-v3.md

@@ -128,7 +128,7 @@ And here's the new look for Dashboard settings:
 
 <img src="/img/docs/v3/dashboard_settings.png">
 
-Check out the <a href="http://play.grafana.org" target="_blank">Play
+Check out the <a href="https://play.grafana.org" target="_blank">Play
 Site</a> to get a feel for some of the UI changes.
 
 ## Improved Annotations

docs/sources/guides/whats-new-in-v4-3.md

@@ -23,7 +23,7 @@ Grafana v4.3 Beta is now [available for download](https://grafana.com/grafana/do
 - New [MySQL Data Source](http://docs.grafana.org/features/datasources/mysql/) (alpha version to get some early feedback)
 - 60+ small fixes and improvements, most of them contributed by our fantastic community!
 
-Check out the [New Features in v4.3 Dashboard](http://play.grafana.org/dashboard/db/new-features-in-v4-3?orgId=1) on the Grafana Play site for a showcase of these new features.
+Check out the [New Features in v4.3 Dashboard](https://play.grafana.org/dashboard/db/new-features-in-v4-3?orgId=1) on the Grafana Play site for a showcase of these new features.
 
 ## Histogram Support
 

docs/sources/guides/whats-new-in-v5.md

@@ -37,7 +37,7 @@ This is the most substantial update that Grafana has ever seen. This article wil
 The new dashboard layout engine allows for much easier movement and sizing of panels, as other panels now move out of the way in
 a very intuitive way. Panels are sized independently, so rows are no longer necessary to create layouts. This opens
 up many new types of layouts where panels of different heights can be aligned easily. Check out the new grid in the video
-above or on the [play site](http://play.grafana.org). All your existing dashboards will automatically migrate to the
+above or on the [play site](https://play.grafana.org). All your existing dashboards will automatically migrate to the
 new position system and look close to identical. The new panel position makes dashboards saved in v5.0 incompatible
 with older versions of Grafana.