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Remove feature flag gitaly_use_resizable_semaphore_lifo_strategy

Emily Chui requested to merge echui/remove-ff-gitaly-use-resizable-semaphore-lifo-strategy into master

This MR will remove gitaly_use_resizable_semaphore_lifo_strategy as this will now be the new default. The feature flag originally controlled the ability to toggle between using a FIFO or LIFO queue in our queing strategy. Now it will default to use LIFO strategy.

The feature flag was turned on Feb 10, 2024. In the following graph (top), the total dropped requests due to max time being reached has decreased since enabling the feature flag. It is more evident with RPCs PostUploadPackWithSideChannel and SSHUploadPackWithSideChannel.

The bottom graph does not show much difference between the two strategies when it comes to dropping requests due to max queue size being reached.

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Looking at the same period where traffic would've been similar, after Feb 10 when the feature flag turns on, the Dropped Requests RPS does seem to go down.

Closes #5919 (closed)

Relates to #5396 (closed). Following the benchmarks extracted about latency in the original issue and the metrics from live traffic, removing the ff and making it the default should be fine.

Edited by Emily Chui

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