[UX] Add a domain/port prefix in the "URL path alias" fields, and remove the help text about not adding a trailing slash

[klonos]

Description of the need

Here's what the field in the "URL settings" tab looks like when creating/editing content:

I have tested adding a path with a leading slash, then with a trailing slash, and then with both. In all cases, the slashes were automatically removed, and the content was saved w/o any errors. The path alias also worked without any issue.

Proposed solution

• Add a protocol/domain/port prefix to the field.
• Remove the "Use a relative path without a trailing slash." bit from the help text, as it provides no value.