am 0884cb5e: am f2b544f5: am 337b0873: docs: update backup guide and bmgr tool elaborate the guide to testing a backup agent and add links between the docs

Merge commit '0884cb5ec6dc425bb3848e682000c1c4b70bc4df'

* commit '0884cb5ec6dc425bb3848e682000c1c4b70bc4df':
  docs: update backup guide and bmgr tool