Add additional exclude property

The default value of `spring.devtools.restart.exclude` is quite long and
any override requires to copy/paste it to add additional exclusions. To
avoid that, a new `spring.devtools.restart.additional-exclude` property
has been added.

Both properties are now used to compute the full list of exclusions that
is used by PatternClassPathRestartStrategy.

Closes gh-3774

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

@@ -627,7 +627,8 @@ content into your application; rather pick only the properties that you need.
     # DEVTOOLS ({sc-spring-boot-devtools}/autoconfigure/DevToolsProperties.{sc-ext}[DevToolsProperties])
     spring.devtools.restart.additional-paths= # additional paths to watch for changes
     spring.devtools.restart.enabled=true # enable automatic restart
-    spring.devtools.restart.exclude= # patterns that should be excluding for triggering a full restart
+    spring.devtools.restart.exclude= # patterns that should be excluded from triggering a full restart
+    spring.devtools.restart.additional-exclude= # additional patterns that should be excluded from triggering a full restart
     spring.devtools.restart.poll-interval= # amount of time (in milliseconds) to wait between polling for classpath changes
     spring.devtools.restart.quiet-period= # amount of quiet time (in milliseconds) required without any classpath changes before a restart is triggered
     spring.devtools.restart.trigger-file= # name of a specific file that when changed will trigger the restart

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -910,6 +910,8 @@ you can use the `spring.devtools.restart.exclude` property. For example, to excl
 	spring.devtools.restart.exclude=static/**,public/**
 ----
 
+TIP: if you want to keep those defaults and _add_ additional exclusions, use the
+`spring.devtools.restart.exclude.additional-exclude` property instead.
 
 
 [[using-boot-devtools-restart-additional-paths]]