Display summary provided by DCR when it has nothing specific to comment on

What does this MR do and why?

Discussed in #538977 (comment 2485869445).

We should display the text within <review></review> tag if it is available and if there were no <comment> tags found in the response. The text will be added to the summary comment.

Before:

I finished my review and found nothing to comment on. Nice work! 🎉

After:

I finished my review and found nothing to comment on. Nice work! 🎉

The changes look good. The MR adds the environment variable `export GITLAB_SIMULATE_SAAS=0` to the documentation for setting up a cloud license via CustomersDot. This aligns with the MR description which mentions that this variable is needed when running a self-managed instance to add subscriptions. The change is straightforward and correctly placed in the documentation.

References

Screenshots or screen recordings

It's hard to get a response from llm which has a summary. So hard code it here:

          def response_body
            ai_response&.dig('content', 0, 'text')
+++            "<review>This MR blah blah...\n<comment file=\"go/server.go\" priority=\"2\" old_line=\"\" new_line=\"16\">\nConsider making the port configurable through an environment variable or command-line flag rather than hardcoding it. This would make the server more flexible for different deployment environments.\n\n<from>\n\tif err := http.ListenAndServe(\":8080\", nil); err != nil {\n</from>\n<to>\n\tport := \":8080\" // Consider using an environment variable here\n\tif err := http.ListenAndServe(port, nil); err != nil {\n</to>\n</comment>\n\n<comment file=\"go/server.go\" priority=\"3\" old_line=\"\" new_line=\"22\">\nThe homeHandler function doesn't handle HTTP methods properly. It should check if the request method is GET and return a 405 Method Not Allowed for other methods.\n\n<from>\nfunc homeHandler(w http.ResponseWriter, r *http.Request) {\n\tif r.URL.Path != \"/\" {\n\t\thttp.NotFound(w, r)\n\t\treturn\n\t}\n</from>\n<to>\nfunc homeHandler(w http.ResponseWriter, r *http.Request) {\n\tif r.URL.Path != \"/\" {\n\t\thttp.NotFound(w, r)\n\t\treturn\n\t}\n\tif r.Method != http.MethodGet {\n\t\thttp.Error(w, \"Method not allowed\", http.StatusMethodNotAllowed)\n\t\treturn\n\t}\n</to>\n</comment>\n\n<comment file=\"go/server.go\" priority=\"3\" old_line=\"\" new_line=\"29\">\nSimilar to homeHandler, helloHandler should also check the request method.\n\n<from>\nfunc helloHandler(w http.ResponseWriter, r *http.Request) {\n</from>\n<to>\nfunc helloHandler(w http.ResponseWriter, r *http.Request) {\n\tif r.Method != http.MethodGet {\n\t\thttp.Error(w, \"Method not allowed\", http.StatusMethodNotAllowed)\n\t\treturn\n\t}\n</to>\n</comment>\n</review>"
          end

click on request review:

now the review looks like:

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Related to #541694 (closed)