Add kubernetes manifests for Heartbeat

[exekias]

Describe the enhancement:

We don't currently offer Kubernetes manifests to deploy Heartbeat. This issues is minded to create and document manifests for Heartbeat like we do for others here: https://github.com/elastic/beats/tree/master/deploy/kubernetes

[elasticmachine]

Pinging @elastic/uptime (:uptime)

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)