Write a blog post for v0.48.9 perf changes (#5206)

Signed-off-by: Shinnosuke Sawada-Dazai <shin@warashi.dev>

docs/content/en/blog/git-operation-performance-improvement.md

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+---
+date: 2024-09-11
+title: "Performance improvement in Git operations on PipeCD v0.48.9"
+linkTitle: "Performance improvement in Git operations on PipeCD v0.48.9"
+weight: 986
+author: Shinnosuke Sawada-Dazai ([@Warashi](https://github.com/Warashi))
+categories: ["Announcement"]
+tags: ["News"]
+---
+
+We have implemented performance improvements for Git operations in PipeCD v0.48.9, which was released on September 10, 2024.
+In this post, we will explain how we enhanced the performance of Git operations in PipeCD and when you can expect to see these improvements in your daily use.
+
+### Background
+
+The PipeCD agent (piped) maintains a git repository cache in the local filesystem to accelerate Git operations.
+When piped needs to clone a repository, it first checks if the repository is already cloned in the cache.
+If the repository is already cloned, piped will fetch the latest changes from the remote repository.
+If the repository is not cloned, piped will clone it from the remote repository.
+Piped uses sync.Mutex to ensure that only one goroutine can access the cache at a time.
+
+### Problem
+
+When multiple deployments are triggered simultaneously within a single repository, piped waits for other goroutines to finish their Git operations
+because sync.Mutex ensures that only one goroutine can access the cache at a time.
+This creates a bottleneck in Git operations, causing delays in deployments.
+
+### Solution
+
+We have improved the performance of Git operations by implementing singleflight.Group from the golang.org/x/sync/singleflight package.
+The singleflight.Group is a package for duplicate function call suppression and caching.
+It provides a mechanism to suppress duplicate function calls, meaning that if multiple goroutines call the same function with the same key, only one call will be made to the function.
+The singleflight.Group also provides a caching mechanism, where the result of the function call is cached and returned to other goroutines that call the same function with the same key.
+We use this singleflight.Group to ensure that only one goroutine can clone the repository from the remote repository, while other goroutines wait for the result of the function call.
+This makes Git operations faster and more efficient, preventing delays in deployments.
+
+### Conclusion
+
+We have enhanced the performance of Git operations in PipeCD v0.48.9 by implementing singleflight.Group from the golang.org/x/sync/singleflight package.
+This improvement makes Git operations faster and more efficient, preventing delays in deployments even when multiple deployments are triggered simultaneously within a single repository.
+You can expect to experience these improvements in your daily use of PipeCD v0.48.9.