Add DRBD dynamic resync speed params to design doc

* Expand the Name column of the table (for c-delay-target)
* Add the c-* DRBDparameters to the table containing the disk parameters
* Add the unit of measurement in square brackets, when needed
* Document the supported DRBD version, warn about the DRBD version
  needed for barriers and for the dynamic resync speed parameters.
* Add links to some documentation about the dynamic resync speed
  parameters

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>