Allow caching based on a configurable number of hits. (#8891)

Co-authored-by: Harshavardhana <harsha@minio.io>

docs/disk-caching/DESIGN.md

@@ -13,16 +13,19 @@ minio gateway <name> -h
      MINIO_CACHE_EXCLUDE: List of cache exclusion patterns delimited by ","
      MINIO_CACHE_EXPIRY: Cache expiry duration in days
      MINIO_CACHE_QUOTA: Maximum permitted usage of the cache in percentage (0-100).
+     MINIO_CACHE_AFTER: Minimum number of access before caching an object.
+
 ...
 ...
 
   7. Start MinIO gateway to s3 with edge caching enabled on '/mnt/drive1', '/mnt/drive2' and '/mnt/export1 ... /mnt/export24',
      exclude all objects under 'mybucket', exclude all objects with '.pdf' as extension
-     with expiry up to 40 days.
+     with expiry up to 40 days. Cache only those objects accessed atleast 3 times.
      $ export MINIO_CACHE_DRIVES="/mnt/drive1,/mnt/drive2,/mnt/export{1..24}"
      $ export MINIO_CACHE_EXCLUDE="mybucket/*,*.pdf"
      $ export MINIO_CACHE_EXPIRY=40
      $ export MINIO_CACHE_QUOTA=80
+     $ export MINIO_CACHE_AFTER=3
      $ minio gateway s3
 ```