[Feature]: support "help" as a subcommand synonymous with "--help"

まだ誰も着手していません。

### Description

Across all the different cloud providers, it becomes easy to forget which option brings up the documentation, manual page, or usage. I frequently find myself typing `linode help`, only to then have to go back and running `linode --help` (or `-h`).

It'd be nice if `help` as a subcommand was synonymous with `--help`. It'd be even nicer if a `help` subcommand brought up a full manual page similar to how AWS cli tools do it. Ideally, you'd then have `linode help` get you the full, detailed manual page in the default pager and `lincode --help` give you the summary of supported command-line options on stdout only.

### Potential Usage Example

_No response_

Start at the CLI entry points that parse ` help`, `--help`, and `-h`, and compare their current behavior. Clarify whether the change is only an alias or also requires a paged manual, then identify the existing CLI checks for help output and verify the agreed behavior for stdout and the default pager.

索引モデルが issue の本文から書いたものです。