chore: add CloudFront cache invalidation for Static Site services

[huanjani]

One of the ways in which CloudFront reduces latency is by caching objects at edge locations, reducing the number of requests that users’ origin servers must respond to directly. For Copilot-managed Static Site services, this caching behavior has the unfortunate side effect of redeployments using cached— and out-of-date— versions of source files. By default, files expire after 24 hours.

We want users to benefit from edge caches, so we don’t want to manage cache expiration by changing TTL values or the cache policy. Instead, we can allow the caching but invalidate the cache each time the Static Site service is redeployed, after (updated) files are uploaded. This way, the updated files are served from the origin server rather than the outdated cached files.

We opted to invalidate all files (/*) for simplicity, efficiency, and cost-savings. If, in the future, customers request the ability to exclude files from invalidation, we can consider adding that config to the workload manifest.

Resolves: #5024.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the Apache 2.0 License.

[github-actions]

🍕 Here are the new binary sizes!

Name	New size (kiB)	size (kiB)	Delta (%)
macOS (amd)	51152	50748	+0.80
macOS (arm)	51336	50956	+0.75
linux (amd)	45032	44680	+0.79
linux (arm)	43332	43012	+0.74
windows (amd)	41872	41548	+0.78

[codecov-commenter]

Codecov Report

Merging #5035 (751910b) into mainline (f111d1b) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           mainline    #5035      +/-   ##
============================================
- Coverage     70.00%   69.97%   -0.03%     
============================================
  Files           291      291              
  Lines         42240    42321      +81     
  Branches        285      285              
============================================
+ Hits          29569    29615      +46     
- Misses        11236    11269      +33     
- Partials       1435     1437       +2     

see 9 files with indirect coverage changes

[dannyrandall]

looks great!!