Improve server-side `assert()` function to TypeScript use

[birdofpreyru]

I guess, we should require the caller to specify expected type of asserted value, and make it clear to TS that this assertion / cast is done there.

react-utils/src/server/utils/errors.ts

Lines 124 to 134 in 73476cb

	export function assert(
	value: unknown,
	schema: joi.AnySchema,
	message = '',
	statusCode = CODES.BAD_REQUEST,
	): void {
	const { error } = schema.validate(value, { abortEarly: false });
	if (error) {
	fail(message.concat(message ? '\n' : '', error.message), statusCode);
	}
	}

Update: After first tests, it seems problematic to do something useful here, both due to peculiarities of TS compiler and its support of asserts feature, and also due to the way express requests are typed.