Wrap `fetch` call in `try/catch`

[david-crespo]

In relatively rare situations and through no fault of ours (like network issues) the fetch call here can throw an error. (One way to repro: turn throttling to Offline in Firefox and submit a form.)

oxide.ts/oxide-api/src/http-client.ts

Lines 146 to 160 in 7890e4d

	public async request<Data>({
	body,
	path,
	query,
	host,
	...fetchParams
	}: FullParams): Promise<ApiResult<Data>> {
	const url = (host || this.host) + path + toQueryString(query);
	const init = {
	...mergeParams(this.baseParams, fetchParams),
	body: JSON.stringify(snakeify(body), replacer),
	};
	return handleResponse(await fetch(url, init));
	}
	}

That means an error of arbitrary shape gets thrown up to the web console, which doesn't know what to do with it, and in fact is not aware that this can happen. In practice, this has been ok because we primarly rely on a message property on our ApiError type which is also present on regular Errors. But it would be nice to be able to explicitly handle non-API errors that occur while making an API call. See oxidecomputer/console#2569.