examples: update gatekeeper auth client to use onError.

[thruflo]

This is what I requested in #2018 (comment)

The client now uses the new onError to handle 401/403 and reconnect with a new auth token.

One observation: with the onError being defined before the shape is instantiated, I'm not sure what the best control flow is to handle a 405 must refetch. Certainly it's hard to handle in the onError callback. I guess this is what's being discussed in #1997 etc.

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[KyleAMathews]

409 must-refetch responses never would reach onError —

electric/packages/typescript-client/src/client.ts

Lines 371 to 377 in e981396

	if (e.status == 409) {
	// Upon receiving a 409, we should start from scratch
	// with the newly provided shape handle
	const newShapeHandle = e.headers[SHAPE_HANDLE_HEADER]
	this.#reset(newShapeHandle)
	await this.#publish(e.json as Message<T>[])
	continue

[thruflo]

So the stream handles it and the shape gets the instruction in a control message?

Makes sense, cool.

[KyleAMathews]

So the stream handles it and the shape gets the instruction in a control message?

yeah exactly — the shape just resets its materialized view and recreates it — subscribers would never notice