Generalize GraphQL args

[wd60622]

Describe what this PR does / why we need it

This generalizes the internals used in the gh.graph function. This allows for some more flexible queries including for list of fields. For instance:

local gh = require "octo.gh"

local query = [[
query($owner: String!, $name: String!, $num_issues: Int!, $states: [IssueState!]) {
  repository(owner: $owner, name: $name) {
    issues(last: $num_issues, states: $states) {
      nodes {
        title
      }
    }
  }
}
]]


gh.graphql {
  query = query,
  fields = {
    num_issues = 10,
    owner = "pwntester",
    name = "octo.nvim",
    states = { "OPEN", "CLOSED" },
  },
  jq = ".data.repository.issues.nodes | map(.title)",
  opts = {
    cb = function(output, stderr)
      vim.print(output)
      vim.print(stderr)
    end
  }
}

Note

This doesn't support passing the whole input for mutations which I elaborate upon in #787

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

Checklist

• Passing tests and linting standards
• Documentation updates in README.md and doc/octo.txt