4.1.0 / 2023-03-20

Codename: They finally made a point release

Small improvements

#264 Add JRuby 9.3 to build matrix: JRuby 9.3 was released, and added as an officially supported version
#273 Add Ruby 3.2 to build matrix: Ruby 3.2 was released, and added as an officially supported version
#280 Optimize incrementing values in DirectFileStore adapter: There were some expensive method calls being made multiple times when they didn't need to be for simple increments. This PR introduces a specialised implementation for that case.
#277 Allow use of instance and job labels: It's now possible to set the instance and job labels on metrics, where previously they had been reserved.

The reason we'd reserved them is that Prometheus automatically generates values for them when it scrapes a target, and we didn't want to cause a collision. It turns out Prometheus handles that collision just fine.

By default, Prometheus server will prepend exported_ to them if they're present in the scraped data (i.e. exported_instance and exported_job). Users can set honor_labels in their Prometheus server config if they prefer the labels from the scraped metric data to take precedence over the labels generated by the server.

#268 Use lowercase response headers in Rack example: Rack 3.0.0 started requiring this for compatibility with HTTP/2
#271 Use lowercase for HTTP headers in middleware: Fixes the same issue from above in our middleware
#270 Small compatibility fixes in Rack example: Apple have taken port 5000 for AirPlay, so we had to move away from it. Go has changed how you install binaries, so we updated those instructions too.