Startup hook should block until URL is loaded

[simonw]

We mostly have a 0.2 second limit on how long we wait for the URL to load.

We should make an exception on startup - because the initial metadata file may include configuration for authentication, which should be loaded before processing any requests.

datasette-remote-metadata/datasette_remote_metadata/__init__.py

Lines 38 to 43 in 3352061

	@hookimpl
	def startup(datasette):
	async def inner():
	await update_remote_with_time_limit(datasette, timelimit=0.2)
	return inner

What should happen if the URL fails to load? Probably should prevent Datasette from starting up at all, but can that plugin hook cancel Datasette's startup by raising an exception?

The documentation suggests that an assert will prevent Datasette starting: https://docs.datasette.io/en/stable/plugin_hooks.html#startup-datasette

[simonw]

I'm going to have timelimit=None mean "wait no matter how long".