Add feature flag for removing CI tool

What does this MR do and why?

CiEditor tool doesn't bring a lot of value and we're going to remove it. Chat is capable of answering those questions without the tool so this change will improve (a bit) performance for users as it skips one request to LLM as well as removes burden of maintaining the tool.

References

Counterpart for gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!1543 (merged) (can be merged independently)

Issue: #495684

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