SITES-26634 [Importer] Labs UI: Allow population of the URLs field from a file

[atopper]

Fix Jira SITES-26634

The command line bulk importer takes a text file full of URLs. Enable that same file to be dropped into the UI, instead of having to copy and paste. Only lines with URLs starting with http will be added. On multiple file drop, only the first file with valid URLs will be used.

Test URLs:

• Before: https://main--helix-labs-website--adobe.aem.live/tools/import/index.html
• After: https://sites-26634-urls-file--helix-labs-website--adobe.aem.live/tools/import/index.html

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Hello, I'm the AEM Code Sync Bot and I will run some actions to deploy your branch and validate page speed. In case there are problems, just click a checkbox below to rerun the respective action.

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Commits

* [ed438ac](https://github.com/adobe/helix-labs-website/commit/ed438aca6de6ecdb11918152a19defe7911c112c) :white_check_mark: (latest) * [e383206](https://github.com/adobe/helix-labs-website/commit/e38320648b136c588c0c0a715c1c32ed01424ec5) :white_check_mark: * [586221b](https://github.com/adobe/helix-labs-website/commit/586221b0606fa08a59608d8a1a191f69f9de6d6f) :white_check_mark: * [d2b0644](https://github.com/adobe/helix-labs-website/commit/d2b06440e59485ab2801eb658012b4c927805139) :white_check_mark:

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