FeedsHTPRequestException failed because its sheme is not supported

Problem/Motivation

Sometimes in the feeds, we can receive URLs (to images for example) with uppercase schema.

The HTTPS://example.com and https://example.com are the same URLs but in the module, the differences are detected as invalid schema.

Steps to reproduce

Here we can try 2 cases:

1) Try to create a feed with HTTPS://example.com/feed.xml URL.
2) Or, you can create a feed with a valid URL, but provide a mapping to upload images from the feed where the path to images will be with uppercase schema.

Proposed resolution

The URL should be converted into a lowercase by default before validation.