Mesos `k8s` plugin support

[algchoo]

Description

This PR updates the Apache Mesos mixin to support the k8s plugin

With the logs being in separate panels for this integration, we're updating the mixin to look for filename or log_type and in the snippets for the k8s plugin we're including log_type as a label for separating the logs.

Changes

• added enableMultiCluster and selectors
• updated mesos dashboard to support k8s plugin
• updated log panel expressions to filter on filename or log_type