feat(examples): enhance the request feature on the examples/discounted-cartrade

[takeutak]

Is your feature request related to a problem? Please describe.
To use examples/discounted-cartrade easily, the http-request feature on the examples/discouted-cartrade is needed.

Describe the solution you'd like
To add http-request feature on the examples/discounted-cartrade

[t-yasushi]

I'm working on this

[t-yasushi]

I issued a PR #1182 to solve part of this issue.
In this PR, I update the cert and private key at default.json to activate trade process in discouted-cartrade.

[t-yasushi]

I issued a PR #1187 to solve the rest of the issue.
I create req_discounted_cartrade.py in example/discounted-cartrade.
This sends http request to discounted-cartrade after resistors indy data.