LUDOC-384 flr: File Level Redundancy (FLR) Documenation

LUDOC-384 flr: File Level Redundancy (FLR) Documenation

This patch creates the initial documentation for the File
Level Redundancy (FLR) feature introduced by LU-9771 in the
Lustre 2.11.0 release.

The FLR feature allows for storing of the same data on
multiple OSTs for a variety of possible benefits and use
cases.

Signed-off-by: Joe Gmitter <joseph.gmitter@intel.com>
Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I4c4ccb9e5c90144f4686e3853d56ebee459cee70
Reviewed-on: https://review.whamcloud.com/31657
Tested-by: Jenkins
Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>