Avoid installing chromium 99 on customer-hosted Looker instances with ubuntu os to prevent rendering issues

[satheeshd]

Chromium is required for scheduling, sending or downloading Looks and dashboards in data formats like PDF or PNG.

On Looker-hosted customer instances, the chromium installation is managed by the Looker team. However, customers need to manage the chromium installation themselves on customer-hosted Looker instances.

Recently, we are facing with rendering pipeline timeouts with chromium 99 when rendering Looks or Dashboards to PDF/PNG format.  However, because of the issue described above, we are now recommending that customers do not install Chromium 99 until this issue is resolved. 

To install a specific version of chromium on Ubuntu, run the following:

$apt-get update && apt-get install -y chromium-browser=<version-number>

Where version-number is the specific version of chromium you want to install on your machine. We recommend installing any of the chromium 98 or less stable releases applicable for your server platform. You find the list of chromium releases on this page: https://chromiumdash.appspot.com/releases?platform=Linux