Increase number of TOC levels to 4 in generated PDF documentation

Closes gh-29781

Author: sbrannen

framework-docs/src/docs/asciidoc/spring-framework.adocbook

@@ -1,5 +1,7 @@
 :noheader:
 :toc:
+:toclevels: 4
+:tabsize: 4
 include::attributes.adoc[]
 = Spring Framework Documentation
 Rod Johnson; Juergen Hoeller; Keith Donald; Colin Sampaleanu; Rob Harrop; Thomas Risberg; Alef Arendsen; Darren Davison; Dmitriy Kopylenko; Mark Pollack; Thierry Templier; Erwin Vervaet; Portia Tung; Ben Hale; Adrian Colyer; John Lewis; Costin Leau; Mark Fisher; Sam Brannen; Ramnivas Laddad; Arjen Poutsma; Chris Beams; Tareq Abedrabbo; Andy Clement; Dave Syer; Oliver Gierke; Rossen Stoyanchev; Phillip Webb; Rob Winch; Brian Clozel; Stephane Nicoll; Sebastien Deleuze; Jay Bryant; Mark Paluch