Promote Helm installation to alpha (#8443)
Promote Helm installation to alpha (#8443)

* Promote Helm installation to alpha

Integration tests have been to master and release-1.8 to support this promotion.

Addressed suggestions made in https://github.com/istio/istio.io/issues/8374

* Minor language fix

* Fixed spelling

* Remove warning for alpha and added link to feature stages doc

* Fix broken link

* Fix formatting
istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io,istio/istio.io