Add more context entry types support

[eddycharly]

Add more context entry types support:

• Add support for context entries from apiCall (HTTP or K8s API) #461
• Add support for context entries from config maps #462
• Add support for context entries from image registry calls #463
• add support for global context #464

[JimBugwadia]

We will need ConfigMap, APICall, ImageRegistry.

We currently have Variable. Can that contain a JMESPath expression or an Assert?

(updated description)

[A-5ingh]

/assign @JimBugwadia and @realshuting I think we should templatize the Issues that contributors raise so that it should have enough information for the beginners at least. Details like brief description, what exactly is happening and what needs to be fixed.