Add staking-miner bin (#7273)

* Add staking-miner bin

* Fix build and doc

---------

Co-authored-by: parity-processbot <>

polkadot/utils/staking-miner/Cargo.toml

+[[bin]]
+name = "staking-miner"
+path = "src/main.rs"
+
 [package]
 name = "staking-miner"
 version.workspace = true

polkadot/utils/staking-miner/README.md

@@ -16,7 +16,7 @@ staking-miner --help
 
 You can build from the root of the Polkadot repository using:
 ```
-cargo build --release --locked --package staking-miner
+cargo build --profile production --locked --package staking-miner --bin staking-miner
 ```
 
 ## Docker