feat(apiSmokeTest): legacy-api-key fallback when TempApiKey is absent

Stacks that have migrated past `apiGateway.apiKeys` in their serverless
config to a Lambda authorizer (which accepts x-api-key via env var)
have no `TempApiKey-*` line in deploy.out. The action's key-extraction
regex misses, `keyMatch` is null, and the action crashes with:

  Could not find key
  TypeError: Cannot read properties of null (reading '0')

apiSmokeTest action
-------------------
- New optional input `legacy-api-key` — used as the x-api-key value
  when the TempApiKey regex misses in deploy.out.
- src/index.js: null-safety on keyMatch and urlMatch; falls back to
  legacy-api-key input when regex misses.
- core.setSecret(key) regardless of source so the value is masked in
  subsequent log output. "Key: …" info line now prints "Key: <masked>".
- dist/index.js + sourcemap rebuilt via yarn build (rollup).

deploy-to-aws-uv.yml
--------------------
- New optional secret `smoketest-legacy-api-key` — passed through to
  the action's `legacy-api-key` input. Callers that have moved past
  TempApiKey can pass their Lambda-authorizer x-api-key value.

Backward-compatible
-------------------
- legacy-api-key defaults to "". Stacks still emitting TempApiKey-* in
  deploy.out work unchanged.

Downstream
----------
- GNS-Science/nshm-toshi-api/deploy-aws-lambda.yaml will pass
  smoketest-legacy-api-key after this lands.

Author: chrisbc

.github/actions/apiSmokeTest/action.yml

@@ -19,6 +19,14 @@ inputs:
   url:
     description: Overwrites URL in case the API cannot be reached through the internal URL (this is the case for our apigw APIs)
     required: false
+  legacy-api-key:
+    description: |
+      Fallback API key value to use as `x-api-key` when serverless deploy output
+      doesn't include a `TempApiKey-…` line (e.g. when the stack has moved past
+      the legacy `apiGateway.apiKeys` config to a Lambda authorizer). Should be
+      passed as a secret. Auto-masked via `::add-mask::` regardless.
+    required: false
+    default: ""
 
 runs:
   using: node20