Consolidate script documentation

Currently there is script related information distributed among these pages

1. https://sling.apache.org/documentation/the-sling-engine/url-to-script-resolution.html
2. https://sling.apache.org/documentation/the-sling-engine/servlets.html
3. https://sling.apache.org/documentation/bundles/scripting.html
4. https://github.com/apache/sling-org-apache-sling-servlets-resolver#bundled-scripts

For 1 most sections apply to both servlets and script therefore I would propose to move the non-script related sections to 2.
The script related sections from 1 should end up in 3 instead.
Also information about the bundled scripts (from 4) should rather be moved to 3.
Afterwards the page at 1 can be removed (redirected to 3)