[5] Kelp GUI: Support delegated signing feature

[nikhilsaraf]

Desired Behavior

I want to use the delegated signing feature offered in Kelp in this issue

Impact

The desired behavior will allow me to run my kelp bot in a public cloud or public KaaS instance without having to share my secret key

Feature Suggestion

We can achieve the desired behavior by adding support for this feature in the Kelp CLI into the Kelp GUI

You can also add a field in the guiConfig.cfg file like DELEGATED_SIGNING_URL to put the URL where to send the delegated signing requests. If this field is present then the GUI will automatically use the delegated signing feature and send to this URL (by manually adjusting the trader.cfg files, or sending as a command-line arg to kelp trade commands when started). If this field is not present the GUI can assume that delegated signing is not being used.
With this approach, the user does not have the option to select delegated signing but is either always enabled or not in KaaS. We can improve access to the delegated signing feature in a later issue.

References

#710