Align TxnKVClient API with client-rust

[marsishandsome]

Current client-java TxnKVClient API is a very different from client-rust. All the following functions are missing:

• put
• get
• get_for_update
• key_exists
• delete
• scan
• scan_keys
• batch_get
• batch_get_for_update
• lock_keys
• send_heart_beat
• gc

We need to add the missing functions.