Non-http protocols returned as invalid links

[tomkiss]

Describe the bug

If I paste a non http-link such as slack://slackinstance.slack.com/archive

The plugin returns that the "Link is not a valid URL". The same happens with ftp://.

This doesn't seem right?

Steps to reproduce

1. Enter a URL using ftp:// or an app specific protocol such as slack:// in to a hyper field
2. Submit and note the returned error-checking

Craft CMS version

5.6.11

Plugin version

2.2.4

Multi-site?

No

Additional context

No response

[engram-design]

This is correct behaviour (for now) where the Yii URL validator in use needs them to be HTTP(S) URL's to be valid. For now, we recommend switching the link type to "Custom".

We'll very likely introduce a setting for URL fields to be more lax on these sorts of URLs, relative URLs and anchor links. There's also plenty of other formats to support.

#188