Make context as the parameter in EntityClient

[wen-hui-sun]

Note

1. Remove the WithContext and Context functions from EntityClient
2. Add context as the first parameter in EntityClient

[allanliu]

Generally LGTM sans the 2 comments. Stamping to unblock.

[jemiahw]

Looks pretty good. One question/comment about query context and the timeout. Good otherwise.

[wen-hui-sun]

Nice catch. I missed that. Allan paying attention! :)
I'm not sure we even want a timeout context here though, do we? I don't think the old code set a timeout here. The server has server side timeout and I don't want the client timing out before the server, although it's not that big a deal. Still, since the old code didn't set a timeout, maybe we continue to not set timeout, but we do pass in the ctx from the Run here.

Replied in #88 (comment)