feat: add add-to-basket cli command

[aleem1314]

Description

Ref: #732

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[aaronc]

I wonder if there's a way to do this without adding this to the proto file

[robert-zaremba]

I second that. Lets don't pollute proto if the only thing we want is to parse helper structure in CLI. And we also don't need proto JSON marshaller for that. The stdlib should work.
In the client/basket package we can just do:

var credits = []basket.BasketCredit{}
bz, err := ioutil.ReadAll(filename)
err = json.Unmarshal(bz, &credits)

so the JSON in the file is an array (without { "credits": ...})

[ryanchristo]

Looks great. Changes to proto definitions are being applied to master as well. We might need to make those changes on master and backport or apply the same changes to master.

[ryanchristo]

I believe we want changes to proto definitions merged into master and backported to the release branch. We will need to add this addition to master as well, correct? @aaronc @technicallyty @robert-zaremba

[robert-zaremba]

I think we can do either way (unless there is a change in state.proto). Those backports needs to be done manually.

[ryanchristo]

Looks good to me.