Allow adding additional tld skip patterns

This commit improves `TomcatEmbeddedServletContainerFactory` so that tld
skip patterns can be set or added to an existing set. An additional
`server.tomcat.additional-tld-skip-patterns` is now being exposed to
easily add patterns via configuration.

Closes gh-5010

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

@@ -201,6 +201,7 @@ content into your application; rather pick only the properties that you need.
 	server.tomcat.accesslog.rename-on-rotate=false # Defer inclusion of the date stamp in the file name until rotate time.
 	server.tomcat.accesslog.rotate=true # Enable access log rotation.
 	server.tomcat.accesslog.suffix=.log # Log file name suffix.
+	server.tomcat.additional-tld-skip-patterns= # Comma-separated list of additional patterns that match jars to ignore for TLD scanning.
 	server.tomcat.background-processor-delay=30 # Delay in seconds between the invocation of backgroundProcess methods.
 	server.tomcat.basedir= # Tomcat base directory. If not specified a temporary directory will be used.
 	server.tomcat.internal-proxies=10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|\\