Pass context for storage operations

[nabokihms]

Is your feature request related to a problem?

It is not related to the particular problem but the design.

Describe the solution you'd like to see

Dex has an interface for a storage. To be able to cancel long-running storage operations, we can pass context to all methods of this interface.

Describe alternatives you've considered

Leave things as they are or add any sane timeout.

Additional context

etcd storage already uses context for its operations.

[PumpkinSeed]

I would like to work on this, but I would like to break it into smaller PRs because it will be a huge change. Breakdown means that PRs for Create, Get, List, Delete, Update - each of these will have one PR. What do you think?

[sagikazarmark]

Sounds good! Thanks for taking the effort.

[bobmaertz]

I'd love to work on this and help push it over the finish line if its available