feat: voting API

[lbiedinger]

• refactor Express API handlers to use single error handler registered as final middleware
• refactor Express API events handlers to be exported as a single router from packages/portal/src/server-middlware/api/events/index.js
• move postgres client helpers for Express API events handlers up the directory hierarchy to be used by other handlers
• introduce a Keycloak client helper for Express API events handlers requiring authorization via Keycloak
• introduce Express API polls handlers for creating, retrieving and deleting votes, exported as a single router from packages/portal/src/server-middlware/api/polls/index.js
• register the polls router at /_api/votes for routes:
  • GET /_api/votes -- fetch votes by external candidate ID, and optional voter if authorization header present
  • PUT /_api/votes/:externalCandidateId -- create a vote for a candidate, scoped to the currently authorized user
  • DELETE /_api/votes/:externalCandidateId -- delete a vote for a candidate, scoped to the currently authorized user
• make FeatureIdeas use the new polls API, passing authorization header on to it, and refreshing access tokens if a 401 response is received

[github-actions]

JIRA ticket: EC-6893

[github-actions]

Preview deployment: https://pr-2419.portal-js.dev.eanadev.org/

[sonarqubecloud]

Quality Gate failed

Failed conditions
74.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud