Spring Security Migrate to io.spring.develocity.conventions plugin

Related gh-15021

See also spring-io/develocity-conventions#82 and spring-io/develocity-conventions#89

Comment From: sjohnr

Note: ~This also solves missing build scans (for example here) after the dependabot update of develocity in gh-15654.~ gh-15654 was instead reverted for now.