[clangd] Set gRPC deadlines to all remote index requests

Summary: "TL;DR: Always set a deadline.", https://grpc.io/blog/deadlines/

Reviewers: sammccall

Reviewed By: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82844