HDDS-16665. Create key should support StoragePolicy

[devmadhuu]

What changes were proposed in this pull request?

Keys now carry a storage policy end to end, so a key's data lands on the storage tier its policy asks for.
Before this change, OM resolved every key's placement to the cluster default. OMKeyRequest.allocateBlock hardcoded it:

// TODO Use the actually passed `allowFallbackStoragePolicy` instead of `true` 
allocatedBlocks = ... .allocateBlock(..., OzoneStoragePolicy.getDefaultPolicy(), true); 
and BlockOutputStream hardcoded the datanode-side storage type, both left as TODOs by HDDS-16388: 

// TODO: Replica to the method parameter
blkIDBuilder.setStorageTypeID(StorageTypeUtils.getID(StorageType.DISK));

This patch resolves all three TODOs. The chain is now:

1. KeyArgs.storagePolicy / KeyInfo.storagePolicy added to OmClientProtocol.proto (fields 25 and 23).
2. OmKeyArgs and OmKeyInfo carry a StoragePolicy, round-tripped through protobuf.
3. OMKeyRequest.getStoragePolicy(bucketInfo, keyArgs) resolves it — key-level policy wins, then the bucket's, then the cluster default — and allocateBlock passes the resolved policy and
   allowFallbackStoragePolicy to SCM. Applied at all three call sites: OMKeyCreateRequest, OMKeyCreateRequestWithFSO, OMFileCreateRequest, OMAllocateBlockRequest.
4. The tier SCM chose reaches the datanode: BlockOutputStreamEntryPool derives a StorageType from OmKeyLocationInfo.getStorageTier(), which threads through BlockOutputStreamEntry →
   RatisBlockOutputStream → BlockOutputStream, populating DatanodeBlockID.storageTypeID and the writeChunkAsync storage type.
5. Client API: OzoneBucket.createKey(key, size, replicationConfig, metadata, tags, storagePolicy), and the policy is readable back via OzoneKey.getStoragePolicy().

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16665

How was this patch tested?

New integration test TestOzoneStoragePolicy (6 tests): explicit key policy honoured, bucket inheritance and key-level override, cluster-default fallback, policy visible to the client on read, FSO bucket path, and empty-key policy recording.

Its datanode assertion checks physical placement, not just metadata:

  assertEquals(expectedStorageType, containerData.getStorageType());                                                                                                                                       
  assertEquals(expectedStorageType, containerData.getVolume().getStorageType());                                                                                                                           
  assertEquals(expectedStorageType, StorageTypeUtils                                                                                                                                                .getStorageTypeFromID(blockData.getBlockID().getStorageTypeID()));   

Co-authored-by: @xichen01