Make "MaxSwallowSize" more easily configurable

See gh-13966

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -263,6 +263,7 @@ content into your application. Rather, pick only the properties that you need.
 	server.tomcat.resource.cache-ttl= # Time-to-live of the static resource cache.
 	server.tomcat.uri-encoding=UTF-8 # Character encoding to use to decode the URI.
 	server.tomcat.use-relative-redirects= # Whether HTTP 1.1 and later location headers generated by a call to sendRedirect will use relative or absolute redirects.
+	server.tomcat.max-swallow-size= # Maximum amount of request body to swallow.
 	server.undertow.accesslog.dir= # Undertow access log directory.
 	server.undertow.accesslog.enabled=false # Whether to enable the access log.
 	server.undertow.accesslog.pattern=common # Format pattern for access logs.