Beats doc updates for 5.6

[dedemorton]

5.6

• Document how to run Beats in a container (Document how to run Beats in a container  #4192)
• Document file permissions for config reloading (Document file permissions for Config Reloading #4189)
• Update screen captures of dashboards.
• [Monica] Add section to upgrading topic about upgrading dashboards to use Kibana API.
• [Tudor] Import machine learning jobs.

NOTE: Moved backlog to #4540

[dedemorton]

Changing this to 5.6 since 5.5 is already out (had to defer some 5.5 work at the last minute because there were higher priority issues in the LS docs).