Module consts

This crate is designed to be at the bottom of the depencey tree to provide common and useful utils and consts to all plugin usage, since plugins crate is at the top depending on crates like frontend and datanode

Constants

• GREPTIME_EXEC_PREFIX
  Greptime preserved metrics prefix
• GREPTIME_EXEC_READ_COST
  Execution cost metrics key
• GREPTIME_EXEC_WRITE_COST