Support for newer Bootstrap versions

[pv42]

Bootstrap 5.3.0 supports color themes (e.g. dark mode), which i would like to use.

Just chanaging the version seems straigtforeward since there seem to be no breaking changes on the code side, but to preserve the access to the old version via the previous util::include APIs I suggest adding new includes for newer versions. The simplest would be adding include_cdn_53() include_cdn_js_53() and include_inline_53().

But adding a Bootstrap version enum as argument to the include version would probably be a better solution.