fix: use array format with x-sentry-auth header for Sentry OTLP (#6079)

Switch from flat object format to array format with explicit
`x-sentry-auth` header name, matching what Sentry's OTLP endpoint
expects.

Previously we used the object format which passes headers as
`OTEL_EXPORTER_OTLP_HEADERS` (flat key=value string). The framework
sends this as an `Authorization` header, but Sentry requires
`x-sentry-auth: sentry sentry_key=...`.

The array format lets us specify the exact header name. Set
`GH_AW_OTEL_SENTRY_AUTHORIZATION` to: `sentry sentry_key=<public_key>`

Author: lpcox

.github/workflows/smoke-otel-tracing.lock.yml

@@ -11,8 +11,10 @@ permissions:
 
 observability:
   otlp:
-    endpoint: ${{ secrets.GH_AW_OTEL_SENTRY_ENDPOINT }}
-    headers: ${{ secrets.GH_AW_OTEL_SENTRY_AUTHORIZATION }}
+    endpoint:
+      - url: ${{ secrets.GH_AW_OTEL_SENTRY_ENDPOINT }}
+        headers:
+          x-sentry-auth: ${{ secrets.GH_AW_OTEL_SENTRY_AUTHORIZATION }}
 
 engine:
   id: copilot