Log number of KVCacheManager blocks at init (#87)

#### Motivation

Users are encountering problems running out of blocks on GPUs with less
than 80GB memory.

#### Modifications

This PR simply adds a print out of the number of free blocks at start-up
time.

#### Result

This will help us debug the issue with users, e.g., we could suggest to
them to change the environment variable
`KV_CACHE_MANAGER_NUM_GPU_BLOCKS` to manually increase the number of
blocks, but we need to first know what they are starting from.

#### Related Issues

https://huggingface.co/ibm-fms/granite-7b-lab-accelerator/discussions/1

Signed-off-by: Thomas Parnell <[email protected]>

Author: tdoublep

server/text_generation_server/models/paged_causal_lm.py

@@ -333,6 +333,9 @@ def __init__(
             total_num_gpu_blocks=total_num_gpu_blocks,
         )
 
+        # log number of free blocks at init
+        print("[PagedKVCacheManager] number of free blocks: %d" % (len(self.kv_cache_manager.free_blocks)))
+
     @property
     def batch_type(self) -> Type[PagedCausalLMBatch]:
         return self._batch_type