Proposed configuration option for better control over hard-coded system messages

[ferenci84]

Validations

• I believe this is a way to improve. I'll try to join the Continue Discord for questions
• I'm not able to find an open issue that requests the same enhancement

Problem

Problem: There are hard-coded system message and there is no way to override.

Why is it a problem:
Reason 1: Some models behave better if we do not add everything possible into the system message.
Reason 2: If the default system message is wrong (which is the case now, as it breaks code formatting), it would be easier to test a better version if there is a way to override
Reason 3: Developers are said to be smart, let's give them more control

Solution

There may be plenty of other solutions, this is just one of them:
A config option, named "replaceSystemMessage" (self-descriptive), default false. This would keep the default behavior as it is now, and let us configure the system message for each model separately.

I have already made the modification, pull request will be done in a moment.

[ferenci84]

I have already made a pull request. I'll continue to work on it based on suggestions.

#3787