Create show command within CLI

[peterbarnett03]

Purpose

We need to create a new top-level show command, to enable uses to easily view their databases and caches. Tables will not be a sub-command, as that remains a SQL query for a database.

Requirements

When a user shows all top-level commands, show should now exist.

Command: show
Description: View all databases and configured caches

$ influxdb3 -h
InfluxDB 3 Core server and command line tools

Usage: influxdb3 [OPTIONS] [COMMAND]

Commands:
  create  Create a resource such as a database or auth token
  delete  Delete a resource such as a database or table
  query   Perform a query against a running InfluxDB 3 Core server [aliases: q]
  serve   Run the InfluxDB 3 Core server
  show    View all databases and configured caches
  write   Perform a set of writes to a running InfluxDB 3 Core server [aliases: w]
  help    Print this message or the help of the given subcommand(s)

Sub-commands are individual issues.

Tasks

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1. Create show databases sub-command within CLI #25745
   v3 +1
2. Create show last-caches sub-command within CLI #25746
   v3 +1
3. Create show meta-caches sub-command within CLI #25747
   v3 +1

[hiltontj]

FWIW - last_caches and meta_caches can be viewed via the system tables in a SQL query, i.e.,

select * from system.last_caches
select * from system.meta_caches

Like SHOW TABLES, that is always within the context of a specific database.

From the CLI, this isn't as convenient as influxdb3 show last_caches, but does offer a lot of flexibility out of the box.

Given that, I think it probably makes sense to have a influxdb3 show tables CLI command if we are going to do it for the caches.