Fix file delivery order

[pzl]

What is the problem this PR solves?

Chunked file delivery would occasionally be delivered out-of-order for certain file sizes

How does this PR solve the problem?

Chunk identifiers (not binary contents, just a few metadata fields) are just manually sorted in code. The positional order is not stored in the chunk documents, only contained in a doc's _id field, which is not a sortable result. Given a upper limit of file size (100mb) and fixed chunk size (4mb), the upper bound for number of documents here is 25. Software sort is reasonable enough

How to test this PR locally

Update securitySolution.maxUploadResponseActionFileBytes in kibana.yml to be 104857600

spin up an endpoint, use the responder console to upload a ~90mb file. The bug reproducing-error is a file hash mismatch. With this fix, hashes will match and the action will be marked success

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

[juliaElastic]

LGTM

[pzl]

buildkite test this

[elastic-sonarqube]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube