This patch fills the following columns in `system.clients` table:
* `connection_stage`
* `driver_name`
* `driver_version`
* `protocol_version`
It also improves:
* `client_type` - distinguishes cql from thrift just in case
* `username` - now it displays correct username iff `PasswordAuthenticator` is configured.
What is still missing:
* SSL params (I'll happily get some advice here)
* `hostname` - I didn't find it in tested drivers
Refs #6946Closes#7349
* github.com:scylladb/scylla:
transport: Update `connection_stage` in `system.clients`
transport: Retrieve driver's name and version from STARTUP message
transport: Notify `system.clients` about "protocol_version"
transport: On successful authentication add `username` to system.clients