Mention available formats and fields in db search command

[ernilambar]

Bug Report

• Yes, I reviewed the contribution guidelines.
• Yes, more specifically, I reviewed the guidelines on how to write clear bug reports.

Describe the current, buggy behavior

Command: wp db search

* [--fields=<fields>]
* : Get a specific subset of the fields.
*
* [--format=<format>]
* : Render output in a particular format.
*

We could improve docs by mentioning what are the available formats and fields like we do in other commands.

Let us know what environment you are running this on

OS:	Darwin 22.6.0 Darwin Kernel Version 22.6.0: Mon Apr 22 20:54:28 PDT 2024; root:xnu-8796.141.3.705.2~1/RELEASE_X86_64 x86_64
Shell:	/bin/zsh
PHP binary:	/usr/local/Cellar/php@8.2/8.2.19/bin/php
PHP version:	8.2.19
php.ini used:	/usr/local/etc/php/8.2/php.ini
MySQL binary:	/usr/local/mysql-8.0.36-macos14-x86_64/bin/mysql
MySQL version:	mysql  Ver 8.0.36 for macos14 on x86_64 (MySQL Community Server - GPL)
SQL modes:
WP-CLI root dir:	phar://wp-cli.phar/vendor/wp-cli/wp-cli
WP-CLI vendor dir:	phar://wp-cli.phar/vendor
WP_CLI phar path:	/Users/nilambarsharma
WP-CLI packages dir:	/Users/nilambarsharma/.wp-cli/packages/
WP-CLI cache dir:	/Users/nilambarsharma/.wp-cli/cache
WP-CLI global config:
WP-CLI project config:
WP-CLI version:	2.11.0