`cargo-pgrx` should be able to use `pgcli`

[Hoverbear]

pgcli is a well known, widely packaged tool for interacting with Postgres ala psql. It would be nice if users could modify their $PGRX_HOME/config.toml and set client = "pgcli" to opt into using pgcli.

[owenthewizard]

Would love this feature!