[0.4.3] Handle empty "" GET /key-shares header parameters better.

Improvements:

• Handle empty ("") x-cdoc2-auth-x5c and x-cdoc2-auth-ticket header parameters better (no long stacktrace in log), return HTTP 400
• Spring Boot 3.4.1 -> 3.4.3 + other dependency updates
• Upgrade dependency ee.cyber.cdoc2.openapi:cdoc2-key-shares-openapi 1.0.1-draft -> 1.0.1 (no changes besides version)

Maven package versions:

cdoc2-shares-server 0.4.3
cdoc2-shares-server-pom 0.2.1
cdoc2-css-db 0.1.3
cdoc2-css-openapi 0.1.2