`gel project init --link` accepts `-I` but ignores it

```
sully@red:~/src/e/tests/gel-toy [json-tweaked*+]
$ gel project init --link -I _localdev
Found `edgedb.toml` in /home/sully/src/e/tests/gel-toy
Linking project...
Specify the name of the Gel instance to link with this project:
>
```

It wants `--server-instance` for what I'm trying to do

Start at the `gel project init --link` command and reproduce the example with `-I _localdev`. Trace how `-I` and `--server-instance` are parsed and passed during linking, then add coverage showing that the provided instance is used instead of prompting for one.

Written by the indexing model from the issue text.