Adjust BlockCacheKey to use the file path instead of file name.

The time-based priority eviction policy relies on the presence of path in the BlockCacheKey to fetch the required metadata to check data hotness and decide whether or not to retain the block in the bucket cache.

Hence, the constructor of BlockCacheKey is adjusted to take the file path as the input parameter. The code paths that create the blockCacheKey and also the unit tests need to be adjusted to pass the path instead of file name.