Add flag for JS enhanced file upload

[DavidBiddle]

The latest version of govuk-frontend (v5.9.0) includes a new JS-enhanced version of the file upload component.

The nunjucks macro has a javascript flag for enabling this:

{{ govukFileUpload({
	id: "file-upload",
	name: "photo",
	label: {
		text: "Upload your photo"
	},
	javascript: true
}) }}

which inserts a div with a class and data attribute around the input element:

<div class="govuk-form-group">
  <label class="govuk-label" for="file-upload-1">
    Upload a file
  </label>
  <div
    class="govuk-drop-zone"
    data-module="govuk-file-upload">
    <input class="govuk-file-upload" id="file-upload-1" name="fileUpload1" type="file">
  </div>
</div>

This PR adds a new javascript flag to the govuk_file_field to accomplish the same thing.

<%= form_builder.govuk_file_field :file,
        id: "file-upload",
	name: "photo",
	label: {
	  text: "Upload your photo"
	},
	javascript: true
%>

[netlify]

👷 Deploy request for govuk-form-builder pending review.

Visit the deploys page to approve it

Name	Link
🔨 Latest commit	a4aaa0a

[peteryates]

Looks great thank you @DavidBiddle - Looking to get the updated versions out this week. I suspect the builds will fail until rebased as there were problems with Rails 7.0.

I started playing around with this in draft form too before I noticed your PR. Closed mine in favour of yours.

[DavidBiddle]

@peteryates thanks for the review! Have accepted your suggestion and rebased