SpringBoot adding and handling 'BOTH' option to 'Banner.Mode' as suggest in #34178

As suggest in #34178, having 'BOTH' option for banner log can be usefull so i added it to the Banner.Mode enum and changing SpringApplication's printBanner() method to handle it.

Comment From: wilkinsona

Unfortunately, I don't think we should make this change. Adding BOTH would mean that we cannot add another mode in the future as it would be unclear to which two modes BOTH applies. Thanks anyway for the PR.