ench: add a better context abstraction

[amalthundiyil]

Currently openelb doesn't have an abstraction to work with the context.Context which can come very handy often. This PR adds a new appctx package along with tests which acts as a better interface to work with context.Context.

Signed-off-by: Amal Thundiyil amal.s.thundiyil@gmail.com

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[ks-ci-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: amal-thundiyil
To complete the pull request process, please assign chaunceyjiang after the PR has been reviewed.
You can assign the PR to them by writing /assign @chaunceyjiang in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment