Add a "list" databases sub-command to the CLI

[peterbarnett03]

Use case:
Knowing what database you're working with is critical to any CLI input, given reading/writing/editing all require knowing its name. However, it can be easily forgotten with no way to discover it again; you can use influxql to show databases, but it requires you entering garbage input for --dbname, which isn't a good practice, plus FlightSQL (default) doesn't currently support a show databases command.

Proposal:
Add a influxdb3 database list sub-command to the CLI which outputs the current database names.

Desired behaviour:

$ influxdb3 database list
Databases
---
field_data
sensor_data

$