feat(dataplane,dashboard): configurable outbound request ID header per project

[olamilekan000]

change adds per-project configuration for the outbound request ID header name (request_id_header), 
defaulting to X-Convoy-Idempotency-Key. 
Webhook deliveries send the event’s idempotency key under that header only 
(no duplicate legacy header when a custom name is set).

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Note

Medium Risk
Changes webhook HTTP headers and tightens event ingestion when custom headers are set; misconfiguration or missing idempotency keys can break subscriber integrations.

Overview
Adds per-project request_id_header (default X-Convoy-Idempotency-Key) so outbound webhook deliveries can expose the event idempotency key under a configurable header name, with dashboard support per the PR description.

API & validation: Project config accepts request_id_header through the API model and persistence layer; test seeds set the default header. Create endpoint event now rejects requests when an outgoing project uses a non-default header name but the event omits idempotency_key (same rule applies in other outgoing event services in this branch).

Tooling: Makefile adds ui-build and ui-build-fresh targets for building the dashboard via scripts/build-ui.sh.

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[mekilis]

Looks ok, but added a few comments. Also, please check the CI; one of the checks failed.

[mekilis]

Two problems. The header only goes out when the event has an idempotency key, so deliveries without one get no Split-Request-ID at all. And when it is sent, the value is that key (usually a ULID), not the UUID their contract specifies. As-is this doesn't meet the contract, which is a stable UUID on every delivery. The value and always-present pieces still need handling.

[mekilis]

root_path flips from /testing to "", which looks like a local debug tweak that got swept in. Unrelated to the feature. Can we drop debug.json from the diff?

[mekilis]

Added comments but please fix the failing tests.

[mekilis]

Still in the diff. Can we revert debug.json to match main?

[mekilis]

This works, thanks. Validating at publish with a 400 across the create paths, plus the dispatcher backstop, is the right call. One ask: add a code comment noting the producer must supply the UUID as the idempotency key, since that's the contract now.

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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