Add redirects to SDK on docs

[vokiel]

SDK moved to doc schema:

https://sdk.ckeditor.com/ => https://ckeditor.com/docs/ckeditor4/latest/examples/index.html
https://sdk.ckeditor.com/index.html => https://ckeditor.com/docs/ckeditor4/latest/examples/index.html
https://sdk.ckeditor.com/samples/*.html => https://ckeditor.com/docs/ckeditor4/latest/examples/*.html

[vokiel]

ErrorDocument 404 https://ckeditor.com/404.html

<IfModule mod_rewrite.c>
    RewriteEngine On

    # Samples
    RewriteRule ^samples/(.*).html$ https://ckeditor.com/docs/ckeditor4/latest/examples/$1.html [R=301,NC,L]
    RewriteRule ^samples/?$ https://ckeditor.com/docs/ckeditor4/latest/examples/index.html [R=301,NC,L]
    # Index
    RewriteRule ^$ https://ckeditor.com/docs/ckeditor4/latest/examples/index.html [R=301,NC,L]
    RewriteRule ^index.html$ https://ckeditor.com/docs/ckeditor4/latest/examples/index.html [R=301,NC,L]

    # All others to 404
    RewriteRule (.*) - [L,R=404]
</IfModule>

# php -- BEGIN cPanel-generated handler, do not edit
# NOTE this account's php is controlled via FPM and the vhost, this is a place holder.
# Do not edit. This next line is to support the cPanel php wrapper (php_cli).
# AddType application/x-httpd-ea-php71 .php .phtml
# php -- END cPanel-generated handler, do not edit