[LFXV2-1194] fix: handle msgpack-encoded v1-objects KV entries

[andrest50]

Summary

• Replace single json.Unmarshal call with a two-step approach: try JSON first, fall back to msgpack if JSON fails
• Add github.com/vmihailenco/msgpack/v5 as a direct dependency
• Update docs to note that v1 KV entries may be JSON or msgpack encoded

Ticket

LFXV2-1194

[Copilot]

Pull request overview

This PR updates the survey service’s v1 NATS KV event handling to support KV entries encoded as either JSON or msgpack, improving compatibility with legacy v1 data formats.

Changes:

• Add a JSON-first, msgpack-fallback decoding path for v1 KV entry payloads.
• Introduce github.com/vmihailenco/msgpack/v5 as a direct dependency (and its transitive go.sum entries).
• Document that v1 KV entries may be encoded as JSON or msgpack.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 3 comments.

File	Description
cmd/survey-api/eventing/kv_handler.go	Implements JSON→msgpack fallback decoding for v1 KV PUT entries and tweaks prefix extraction.
docs/event-processing.md	Documents that v1 KV payloads may be JSON or msgpack and describes the fallback behavior.
go.mod	Adds msgpack dependency (and updates direct/indirect requirements).
go.sum	Records checksums for the newly added msgpack dependency and transitive modules.

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[mauriciozanettisalomao]

Approved.

Maybe in the next PR, we can add a revive.toml to remove some lint warnings that we don’t usually address in the code anyway, like package-comments.

[andrest50]

Approved.

Maybe in the next PR, we can add a revive.toml to remove some lint warnings that we don’t usually address in the code anyway, like package-comments.

Thanks. Yeah we can have a revive.toml file. The megalinter errors are so widespread and mostly irrelevant that I've let the check fail for a while now. I need to address that in a PR with a megalinter config that works for this codebase.