Add sls config commands

This is a Feature Proposal

Description

PR #3558 recently added support for a .serverlessrc file. This file will now hold the configured serverless platform credentials and other config info. We should add generic config commands for managing these files in a programmatic way.

• Take care of file permission handling (e.g. check when file is read)

.serverlessrc file format

The .serverlessrc format is JSON.

Commands to support

sls config set -k <key> -v <value> [-g|--global]

• Sets a config value in .serverlessrc.
• Defaults to setting values at the project level (cwd).
• To set a value at the global level (~/.serverless/.serverlessrc) use the -g option.
• Creates a .serverlessrc file if one does not exist.
• Since the config file is json, key depth can be specified using .
  • Example: running sls config set -k foo.bar -v hello results in…

{
  "foo": {
    "bar": "hello
  }
}

• Command should return success message

Successfully configured ~/path/to/.serverlessrc
<key>: <value>

sls config get -k <key>

• Gets a config value
• Key depth can be specified using .
• Command outputs value found at key

sls config delete -k <key> [-g|--global]

• Deletes a config value
• Executes at the project level by default
• Key depth can be specified using .
• Command outputs value deleted at key
• To delete a value at the global level (~/.serverless/.serverlessrc) use the -g option.

sls config list

• Lists all config from both the project and global levels
• Command outputs…

Global config `~/.serverless/.serverlessrc`
{
  "foo": "bar"
}

Project config 
Global config `~/path/to/project/.serverlessrc`
{
  "bar": "baz"
}

[HyperBrain]

Could we support YAML and JSON for the rc file? With the parser that is used in SLS this should work easily. (see my PR to add something similar for the serverless.yml/yaml/json here https://github.com/serverless/serverless/pull/3647). There is even no need to support file endings in this case - the .serverlessrc’s name is fix - but if the yaml parser is used it will support both right away.

[brianneisler]

@pmuens no skeleton or default config at the moment. Simply create an empty json file and add the config being set by the command.