Reduce memory used by highlighting cache
What does this MR do and why?
- Set a smaller TTL for highlighting diffs cache (1 day instead of 7 days). The average idle time for the key is about 6 hours. Let's try and set smaller TTL to reduce memory consumption.
- Use SHA for diffs highlighting cache keys. Currently, we use plain Ruby hash as a part of a key, but calculating the SHA from it and using the value instead is better from the memory perspective
Related issue: #367160 (comment 1026589608)