Create runner(s) to ensure that the Diagnostics Events API is working end to end

The Portal is taking a dependency on the Diagnostics Events API to notify the user about issues that affect their function app. We need to ensure that the Diagnostics Events API is working end to end.

/cc @soninaren @eamonoreilly @FinVamp1

The issue names the Diagnostics Events API and its Portal dependency but does not identify files, tests, or entry points. Start by locating the API implementation and the Portal integration, then determine how an end-to-end runner should exercise them. Done means the runner verifies that diagnostics events reach the Portal as expected.

Written by the indexing model from the issue text.