Data Explorer can run arbitrary SQL queries which can be costly for us if over-used. Because of that we want to add the ability to rate limit the query run endpoint, in particular when requested programmatically using API.
This commit introduces a rate limit to the `QueryController#run` endpoint. It heavily leans on the existing `RateLimiter` implementation, and the ability of `ApplicationController` to turn rate limit exceptions into nicely formatted JSON responses.
The rate limit (per 10 seconds) can be configured through the global setting `max_data_explorer_api_reqs_per_10_seconds`, and defaults to 2.
Handling can be configured through `max_data_explorer_api_req_mode`, and can be set to warn, block, or both warn and block. We will default to warn for now and monitor the logs for a while.
This commit updates the plugin to the latest guidelines, as shown in
discourse-plugin-skeleton, which involves moving a lot of the code to
dedicated files, use proper namespaces, use the autoloader as much as
possible, etc.
Ted Johansson
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