[v1.5] add timeout to etcd member add

[kinarashah]

Issue: rancher/rancher#43356

• Etcd client v3 kept retrying on member add vs v2 client used to return errors so we didn't have timeout earlier
• DialTimeout alone doesn't suffice, also need to specify client request timeout with context
• Updated to close all etcd clients as v3 client uses grpc to connect to etcd, could leave us with leaks if not closed

[zmedico]

Hi, I've also experienced etcd scaling issues with rancher-2.8.x that I did not experience with rancher-2.7.x, and this timeout for the v3 etcd client looks very promising, thanks!