Default params values are not written into config

[MaksymZavershynskyi]

When user does not specify param value that has a default value (e.g. https://github.com/near/rainbow-bridge-cli/blob/9706e057dae85127901c2591090f16d2071ebff4/index.js#L161), the default value is not written into config.

Apparently, it is a quirk of commander. It does not call a custom argument handler https://github.com/near/rainbow-bridge-lib/blame/master/config/index.js#L46 when argument has default value but user does not override it. Which means that this code here is probably not executed https://github.com/near/rainbow-bridge-lib/blame/master/config/index.js#L66

The workaround would be to pre-populate this.paramValues with default values when command is executed.

Note, populating default params in maybeGetParam will not work because not all params are guaranteed to be accessed by the command.