Move internal enrichment files to fb/ for OSS exclusion (#5541)

Summary:
Pull Request resolved: #5541

X-link: https://github.com/facebookresearch/FBGEMM/pull/2508

CONTEXT: Several enrichment files in dram_kv_embedding_cache depend on
internal Meta APIs (opentab, maple, laser, servicerouter, feature_store)
but were being synced to the public pytorch/FBGEMM GitHub repo. This
forces anyone changing these internal APIs to go through the GitHub sync
process unnecessarily, since these files are dead code in OSS.

WHAT: Move 6 internal-only enrichment files from src/dram_kv_embedding_cache/
to fb/src/dram_kv_embedding_cache/ so they are excluded from OSS sync.
Update all #include paths and BUCK target references accordingly.

Files moved:
- oneflow_enrichment.cpp (depends on opentab/maple)
- oneflow_enrichment.h
- opentab_backend_registry.h
- feature_store_enrichment.cpp (depends on servicerouter/feature_store)
- feature_store_enrichment.h
- igr_enrichment.h (depends on laser)

Reviewed By: emlin

Differential Revision: D98357970

fbshipit-source-id: 0426f86bc98bd9ba3d41f5e81736aa43691a3eed

Author: EddyLXJ

fbgemm_gpu/src/dram_kv_embedding_cache/dram_kv_embedding_cache.h

@@ -30,13 +30,13 @@
 #include "../ssd_split_embeddings_cache/initializer.h"
 #include "../ssd_split_embeddings_cache/kv_db_table_batched_embeddings.h"
 #include "SynchronizedShardedMap.h"
+#include "deeplearning/fbgemm/fbgemm_gpu/fb/src/dram_kv_embedding_cache/feature_store_enrichment.h"
+#include "deeplearning/fbgemm/fbgemm_gpu/fb/src/dram_kv_embedding_cache/igr_enrichment.h"
+#include "deeplearning/fbgemm/fbgemm_gpu/fb/src/dram_kv_embedding_cache/oneflow_enrichment.h"
 #include "enrichment_config.h"
 #include "fbgemm_gpu/split_embeddings_cache/kv_db_cpp_utils.h"
 #include "feature_evict.h"
-#include "feature_store_enrichment.h"
 #include "fixed_block_pool.h"
-#include "igr_enrichment.h"
-#include "oneflow_enrichment.h"
 
 namespace kv_mem {