Add a helper for quickly exporting without creating export for a model

[skills-up]

1️⃣ Why should it be added? What are the benefits of this change?
Allows to quickly export from a controller without creating the export specific to a model/query. E.g.,

$query = Comment::with('post')->where('user_id', auth()->user()->id);
$headings = [
  'post.title' => 'Post Name',
  'content' => 'Comment',
  'created_at' => 'Date/Time',
];
return Excel::download(
  new GenericQueryExport($query, $headings),
  'activities.csv',
  \Maatwebsite\Excel\Excel::CSV
);

2️⃣ Does it contain multiple, unrelated changes? Please separate the PRs out.
No

3️⃣ Does it include tests, if possible?
No

4️⃣ Any drawbacks? Possible breaking changes?
Makes assumptions about relations already included in the query, and single header row

5️⃣ Mark the following tasks as done:

• Checked the codebase to ensure that your feature doesn't already exist.
• Take note of the contributing guidelines.
• Checked the pull requests to ensure that another person hasn't already submitted a fix.
• Added tests to ensure against regression.

6️⃣ Thanks for contributing! 🙌

[patrickbrouwers]

Hey, thanks for your PR. Unfortunatly this is not something I'm looking for to merge.

We already have a shortcut to quickly export queries, by doing the macro:

User::query()->downloadExcel('query-download.xlsx', Excel::XLSX, true);

[skills-up]

Wouldn't your way still require an export to be defined specifically for the query?
Otherwise, User::query()->downloadExcel() would result in:

BadMethodCallException  Call to undefined method Illuminate\Database\Eloquent\Builder::downloadExcel(

[patrickbrouwers]

Sorry I forgot I hadn't tagged that release yet. It's part of 5.1.53 version

[skills-up]

Perhaps docs need to be updated for the same.

[patrickbrouwers]

Docs are updated. Perhaps PWA cache why it doesn't show up yet: https://docs.laravel-excel.com/3.1/exports/from-query.html