[proposal] Add an endpoint that crashes

[leplatrem]

Adding a crashing endpoint to our services could help us make that the service monitoring (logging and graph of 5XX responses) and error reporting (Sentry, slack notifs) is configured correctly.

@app.route("/__crash__")
def crash():
    logger.error("about to boom")
    raise ValueError("boom")

[leplatrem]

I see here that @jwhitlock and @willkg proposed a __broken__ endpoint for this

[willkg]

I threw that confluence page together based on what @jwhitlock and I have done in the past because nothing existed and I needed something to point to. I'm game for changing the endpoint to a name that makes more sense.

Also, it should be behind basicauth or require a superuser so it doesn't allow people to spam our Sentry instance.

[pjenvey]

+1 we (push/sync/merino/etc) use an /__error__ endpoint for this