Implement new error structure in backend.

[kgodey]

Problem

We've agreed on a standard error structure for the API in #560. Now we need to implement it.

Proposed solution

I'll format these in terms of desired outcomes. Whoever works on this can feel free to split these up into separate issues if that's helpful.

• All current API error responses should follow our error structure.
• All error codes and their corresponding details fields are documented somewhere.
• We have a standard way of generating new error codes.

Additional context

• Define common error structure #560
• API Standards wiki page

[silentninja]

I am planning to set up the necessary infrastructure so that it is easier to capture and define the error structure for the captured error. Which it be then followed by each error getting then own error structure(sub tasklist), where #859 will be the priority

[silentninja]

Though we can complete this issue by fixing the returned error response, I think it would be better if #623 is completed before we make changes to the structure of the error response as it will be easier to organise and define them.

[kgodey]

@silentninja That's fine. please make small and incremental PRs so that changes are easy to review and merge. Getting #859 done to unblock the frontend soon should be a priority, so please organize your work so that we get to that ASAP.

[silentninja]

@kgodey I put together a meta issue #889 that composes all the requirements for error handling.

[kgodey]

Thanks @silentninja