Use a patched version of nlohmann::json

[iskakaushik]

No description provided.

[rschu1ze]

nlomnann::json is a dependency of ai-sdk-cpp. From the perspective of ClickHouse as the top-level directory, it is a recursive dependency (a dependencies' dependency). Doing so technically discouraged. It would be nicer if nlohmann::json could be moved into its own fork repository, so that directory contrib/ looks like this:

• ai-sdk-cpp
• ai-sdk-cpp-cmake
• nlohmann
• nlohmann-cmake

Maintaining nlohmann::json in its own fork repository makes it easier to maintain custom patches (like done here) in the long run.

[rschu1ze]

Note that another copy of nlohmann::json is being imported as a dependency at the moment (ClickHouse/ClickHouse#82881 (comment)). The one here is being renamed to _patched.