Add config new command to create new config file

[waldekmastykarz]

Add a new command named config new that creates a new config file in the current directory.

devproxy config new -n,--name [name]

• if no file name specified, uses devproxyrc.json
• if a file with the same name exists, adds a number until a unique name found, eg devproxyrc_2.json
• proposed file contents:

{
  "$schema": "https://raw.githubusercontent.com/microsoft/dev-proxy/main/schemas/v0.18.0/rc.schema.json",
  "plugins": [
  ],
  "urlsToWatch": [
    "https://api.contoso.com/*"
  ],
  "logLevel": "information",
  "newVersionNotification": "stable"
}

[waldekmastykarz]

@microsoft/dev-proxy-maintainers do we cover it all? Anything else that we should consider?