Support graphql inputs as lua tables

[wd60622]

Following #782, I would like to better support graphql inputs in mutations. For instance,

local mutation = [[
mutation($star_input: AddStarInput!) {
  addStar(input: $star_input) {
    starrable {
        id
    }
  }
}
]]

local addStarInput = {
    starrableId = "..."
}


gh.graphql {
    query = mutation, 
    fields = {
        star_input = addStarInput
    }
    ..., 
}

However, this can currently be done like this which might be more verbose:

local mutation = [[
mutation($starrableId: ID!) {
  addStar(input: {
    starrableId: $starrableId
  }) {
    starrable {
        id
    }
  }
}
]]

local starrableId = "..."


gh.graphql {
    query = mutation, 
    fields = {
        starrableId = starrableId
    }
    ..., 
}

Reference: https://docs.github.com/en/graphql/reference/mutations#addstar

[wd60622]

Examples of where this would be used:

• Issues: https://github.com/wd60622/octo.nvim/blob/422ad579eca0eba1d26fbcec28ed0af6c8747f65/lua/octo/pickers/telescope/provider.lua#L144-L144
• Pull Requests: https://github.com/wd60622/octo.nvim/blob/422ad579eca0eba1d26fbcec28ed0af6c8747f65/lua/octo/pickers/telescope/provider.lua#L295-L295