Feature: OverrideConfig allows partial override

[mokeyish]

with this PR, we can set partial value. no need to set full config.

• case 1:

  curl http://127.0.0.1:8711/api/v1/prediction/be46c4d4-52cf-4d1b-9a76-c195643dfa0b \
    -X POST \
    -d '{"question": "Hey, how are you?", "overrideConfig": {"config": {"ver":123} }}' \
    -H "Content-Type: application/json"
  # output
  # {"text":"\nver: 123\nurl: http://google.com\n","chatMessageId":"e0dfb81a-99d2-4e8a-b2e4-28bd73e769a2","chatId":"7e38918a-a037-46a8-a964-7e0d3abe6cf1"}
  

• case 2:

  curl http://127.0.0.1:8711/api/v1/prediction/be46c4d4-52cf-4d1b-9a76-c195643dfa0b \
    -X POST \
    -d '{"question": "Hey, how are you?", "overrideConfig": {"config": {"url": "https://github.com"} }}' \
    -H "Content-Type: application/json"
  # output
  # {"text":"\nver: 12345\nurl: https://github.com\n","chatMessageId":"e0dfb81a-99d2-4e8a-b2e4-28bd73e769a2","chatId":"7e38918a-a037-46a8-a964-7e0d3abe6cf1"}
  

[HenryHengZJ]

thanks @mokeyish !!

For future reference:

1.) Have a Custom JS Function node with multiple Input Variables:

2.) When calling API with overrideConfig, with only 1 input variable is provided

{
    "question": "hello!",
    "overrideConfig": {
        "functionInputVariables": {
            "character": "sarcastic"
        }
    }
}

This will results in error saying another variable (in this case $action) is not defined

3.) This PR fixes that