Read pool demand

Returns the token's pool, its oldest queued jobs (routing facts only) and its running job count, for reconciliation, with an ETag. With If-None-Match set to an earlier reply's ETag and wait, the request is held until the demand differs from that reply or wait seconds pass; 304 means nothing changed. An app installed as a runner provider names the pool with pool and authenticates with an installation token holding org:runners (read or write) on the pool's organization; a pool it cannot read is 404.