Add Instructions Detailing Servlet Path Declaration in Migration Guides

[jzheaux]

https://docs.spring.io/spring-security/reference/migration-7/web.html#_include_the_servlet_path_prefix_in_authorization_rules is intended to alert applications that they need to now specify the servlet path in each authorization URI pattern.

It does not describe that Security supports configuring a global servlet path by publishing your own PathPatternRequestMatcher.Builder bean:

@Bean
PathPatternRequestMatcher.Builder requestMatcherBuilder(PathPatternParser mvcPatternParser, DispatcherServletPath servletPath) {
	PathPatternRequestMatcher.Builder builder = new PathPatternRequestMatcher.withPathPatternParser(mvcPatternParser);
	String path = servletPath.getPath();
	return ("/".equals(path)) ? builder : builder.basePath(path);
}

The migration guide should be updated to demonstrate and explain this.