Add a command in birdwatcher, get stats of files in etcd

[jiaoew1991]

can we add a command in birdwatcher, get stats of files in etcd.
Like:

How many delta logs are there in total, how many stats logs are there in total?
This might be very important for such use cases.

Also we need to think of how to handle these bugs

Originally posted by @xiaofan-luan in milvus-io/milvus#28549 (comment)

[MrPresent-Han]

/assign MrPresent-Han