Add Contexts API

[NivLipetz]

Is your feature request related to a problem? Please describe.
Predator is missing the functionality of grouping resources (tests/reports/jobs) to different contexts (teams, users, organizations, etc).

Describe the solution you'd like
In order to add this desired groupings so it's easier to filter and divide the resources into more relevant subgroups, a new resource context needs to be defined.

1. Define new contexts API
   • POST /v1/contexts
   • GET /v1/contexts
   • DELETE /v1/contexts/{contextID}
2. Context should be a simple list of values saved in the db (create new contexts table) with the following fields:

id: STRING (primary key - string)
name: STRING

3. Limitations: name and id should be unique => can't create a context with the same name of one that's already created (return 400 BAD_REQUEST in this case).

Additional context
Use the following file structure as a guide on how to create this new API and resource in Predator's architecture:
https://github.com/Zooz/predator/blob/master/CONTRIBUTING.md#system-resource-folder-structure

[sprakash57]

May i take this up?

[NivLipetz]

Hi @sprakash57 that would be great! We are available on our slack workspace for any questions.

[sprakash57]

Sure.

[sprakash57]

@NivLipetz I saw @tomcorey26 already raised a PR against it. Let me know if it needs additional work.

[NivLipetz]

Hi @sprakash57 I see that someone raised a PR against this issue already although it was assigned to you.. Sorry about that.

Moving forward, if you like there's an open issue that integrates this context_id to all of the other relevant Predator resources (tests, jobs, reports, etc). It's an issue with the same amount of code needed to be complete as this one. Take a look maybe you will find it suiting 😄 #495

[sprakash57]

@NivLipetz can you assign #495 to me?

[NivLipetz]

@sprakash57 can you please request on the issue itself? won't let me assign you otherwise