Connecting via password to a Gel instance will default the user to `edgedb`

See https://github.com/geldata/gel-cli/blob/b782560ba18b5429aceb0094e8acf5d57a6cba8e/src/options.rs#L1045

This should be server version dependent I think? Not sure if we can know this ahead of time, but either way, this is confusing given that the new default is "admin" not "edgedb".

Start in src/options.rs around line 1045, where password connections default the user to `edgedb`. Investigate whether the server version is available before selecting the default, and define behavior for versions using `edgedb` versus `admin`. Done means the password connection no longer presents a confusing default for the server version.

Written by the indexing model from the issue text.