Add a valid API key

[soulgalore]

Since WebPageTest became WebPageTe$t we don't have a valid API key. Either we could pay $15 per month (if 1000 tests will do) or deploy our own version of the Apache branch but I want to avoid adding more server costs to the project.

[soulgalore]

enhanced :D

[2021-09-10 12:00:06] ERROR: Could not run test for WebPageTest {"statusCode":400,"statusText":"Invalid API key. To continue running tests via the WebPageTest API, you'll need to update your current key for the enhanced WebPageTest API. Read more here: https://product.webpagetest.org/api"}