[RRFC] Add method for getting help on config option

Motivation ("The Why")

Some configuration keys are not self-explanatory by their name. This will require someone to search up the configuration name online. A faster and simpler way that can even work offline would be to add in a help method on the npm config command in the CLI. I am aware of the npm help 7 config command, but that gives extra information for each configuration key. A method to get the help output for a single configuration key would be much more useful.

Example

$ npm config help also

- Default: null
- Type: String

When "dev" or "development" and running local npm shrinkwrap, npm outdated, or npm update, is an alias for --dev.

$ npm config help init-author-name

- Default: ""
- Type: String

The value npm init should use by default for the package author's name.

$ npm config help loglevel

- Default: "notice"
- Type: String
- Values: "silent", "error", "warn", "notice", "http", "timing", "info", "verbose", "silly"

What level of logs to report. On failure, all logs are written to npm-debug.log in the current working directory.

Any logs of a higher level than the setting are shown. The default is "notice".

$ npm config --help

npm config set <key> <value>
npm config get [<key>]
npm config delete <key>
npm config help <key>
npm config list [--json]
npm config edit
npm set <key> <value>
npm get [<key>]

alias: c

As seen above, the help output gives details on the key.

How

• Store the help output that will have to be returned for each key
• Log the output when the CLI asks for it

Current Behaviour

No help command on config.

Desired Behaviour

There is a help command on config.

References

• https://docs.npmjs.com/cli/v6/using-npm/config
• https://docs.npmjs.com/cli/v6/commands/npm-config

Start with the npm config CLI entry point and the referenced npm config documentation. Determine how configuration-key help is stored and how the command should format and return one key's details, including unknown-key behavior. Done means npm config help provides the requested details and npm config --help documents the command.