[5.x] Fix broken docs URLs; rename docs URL redirect to permalink

[rob]

There were two templates not referencing the docs URL correctly:

• resources/views/assets/index.blade.php
• resources/views/collections/empty.blade.php

These show up like this (using Collections as an example):

For example:

@include('statamic::partials.docs-callout', [
    'topic' => __('Assets'),
    'url' => 'assets'
])

Instead of:

@include('statamic::partials.docs-callout', [
    'topic' => __('Assets'),
    'url' => Statamic::docsUrl('assets')
])

In addition, resources/views/collections/index.blade.php was set up correctly, but pointing to https://statamic.dev/collections-and-entries which just redirects to https://statamic.dev/collections. This changes that so it's uniform with the empty.blade.php changes.

[duncanmcclean]

Thanks!