chore(docs): Update cStor user guide

[anupriya0703]

• [x] Update the user guide contents, replacing SPC contents with CSPC.
• [x] Changed/updated sub-sections under this PR-
  • Expanding a cStor volume
  • Performance Tunings in cStor Pools
  • Snapshot and Clone of a cStor Volume
  • Creating cStor storage pools
  • Creating cStor storage classes

Signed-off-by: anupriya0703 anupriya.gupta@mayadata.io

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