web/settings: wire pipeline secrets to the spindle xrpc
Adds a spindle service-auth client and wires the pipelines secrets section
(list/add/remove) to sh.tangled.repo.*Secret; spindle selection stays a
read-only display (it is a repo-record edit, not a spindle call).
Signed-off-by: Anirudh Oppiliappan <anirudh@tangled.org>