feat(testitall): Webhook Auth and Resp Sizes Cumulative Updates

[jnxyp]

• updated webhook auth endpoints to support new auth types, and return more helpful error/success messages
• replace all the payload strings to randomly generated string to avoid being compressed
• renamed the endpoint /context-too-large to /response-too-large, as it is used to test the extension call response size limit (100KB)
• changed the endpoint /context-almost-too-large to return a response with size of 65KB, which is half of the session size limit (~130KB)
  • updated the Test handle an almost too large response for context storage action to save the response to session twice to trigger the session size limit error
• added endpoint /webhook/headers for testing webhook with custom headers
• added endpoint /webhooks/error/too-large for testing too large (>4MB) responses from webhooks
  • size controlled by env var WEBHOOK_RESPONSE_SIZE_LIMIT
• added endpoint /webhooks/large for testing large (~3.9MB) responses from webhooks
• for oauth custom flow, now also checking for apikey_id=WA_CUSTOM_APIKEY_ID
• added endpoint /test/stream/json for testing streaming responses with json objects
• updated testitall.actions.json and testitall.openapi.json to include the changes above