Compiler: add default export even if there's an export already in the code (strict check for default export, not just /export/)

Description.

Runtime seems to always require a compiled job to have a default export of an array. Hence, those without a default export break the runtime.

Because

1. we access the default export.
   https://github.com/OpenFn/kit/blob/4376f7b3e615c0b0144deecf6d65d4a03dbb3abf/packages/runtime/src/execute/expression.ts#L146
2. we expect an array and want to iterate it
   https://github.com/OpenFn/kit/blob/4376f7b3e615c0b0144deecf6d65d4a03dbb3abf/packages/runtime/src/execute/expression.ts#L53

Currently,

We create a default export and then put all top-level-expressions in it. If there's no top-level-expression and empty array is exported to make the runtime happy.

export default []; // to make runtime happy!

But,

when there's an export (either named or not) that isn't a default export, we ignore the creation of the default export which makes the runtime sad.

There might be programs to be run in this job but because of a single non-default export. They don't get executed.

eg.

import {fn} from "@openfn/common"

fn(state => {
  state.data.name = "doc-han"
  return state;
})

export const han = "Han"; // prevents our runtime from running

fn(() => {
  state.data.isGithub = true;
  return state;
})

Is there a reason we don't accommodate this? @josephjclark
I feel we can have other exports and still generate our default export. Also, if the user provides a default export(which isn't encouraged) we can also check if it exports an Array.

Here we do a regex match.
https://github.com/OpenFn/kit/blob/4376f7b3e615c0b0144deecf6d65d4a03dbb3abf/packages/compiler/src/transforms/ensure-exports.ts#L15

For the concern of having several types of export nodes. A default export seems to always have only one type of Node representation. The name of the node only changes across ast-generator.

Proposed solution.

1. Instead of regex matching the type 'Export ', Look for default export node instead.
2. check if the default export node has declaration that's an Array