Bucket: Add timeout to thanos bucket inspect

[jdfalk]

Thanos, Prometheus and Golang version used

buildsys:~/repos/gocode/src/github.com/jdfalk/thanos$ ./thanos --version
thanos, version 0.7.0 (branch: master, revision: bfb5645)
build user: builduser@buildsys
build date: 20190917-13:59:50
go version: go1.13

What happened
thanos bucket web supports a timeout value but thanos bucket inspect does not.

What you expected to happen
Both would have timeout options.

How to reproduce it (as minimally and precisely as possible):
Default build

Anything else we need to know
I'll create a pull request to add the feature.