feat(grafana): adding basic grafana dashboard

[pawanpraka1]

Fixes: #93

adding grafana dashboard for following metrics :-

Volume Capacity (used space percentage)
ARC Size, Hits, Misses
L2ARC Size, Hits, Misses
ZPOOL Read/Write IOs
ZPOOL Read/Write time

Reference has been taken from : - https://grafana.com/grafana/dashboards/7845

Signed-off-by: Pawan pawan@mayadata.io

[codecov-io]

Codecov Report

Merging #110 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #110   +/-   ##
=======================================
  Coverage   22.90%   22.90%           
=======================================
  Files          14       14           
  Lines         489      489           
=======================================
  Hits          112      112           
  Misses        376      376           
  Partials        1        1           

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[kmova]

@pawanpraka1 as part of this PR, can the following also be done:
(a) Include the capacity status - total capacity vs used vs available.
(b) Add a json comment indicating that this was inspired from the chart link (mentioned in PR)
(c) update monitoring instructions for setting up this Grafana dashboard. (Even if a link to this sample file.)

[pawanpraka1]

@kmova, learning how can I add more parameters. Will add the details once I figure this out.