multiple expiring system messages (#110, #112)

[mawinter69]

You can now define multiple system messages. Each message can have an expiration time. Messages can be dismissed on a per user basis.

fixes #112
fixes #110

Testing done

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[jonesbusy]

Just updated the plugin, looks I cannot add anymore system message (via JCasC or UI)

jenkins        |        at java.base/java.lang.Thread.run(Unknown Source)
jenkins        | Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Set.removeIf(java.util.function.Predicate)" because the return value of "io.jenkins.plugins.customizable_header.UserHeader.getDismissedMessages()" is null
jenkins        |        at io.jenkins.plugins.customizable_header.CustomHeaderConfiguration.getSystemMessages(CustomHeaderConfiguration.java:143)
jenkins        |        at io.jenkins.plugins.customizable_header.headers.SystemMessageProvider.getSystemMessages(SystemMessageProvider.java:9)
jenkins        |        ... 154 more
jenkins        |  
jenkins        | [2024-06-03T13:34:06.103+0000] [WARNING] hudson.ExpressionFactory2$JexlExpression evaluate # Caught exception evaluating: instance[name] ?: attrs.default in /manage/appearance/. Reason: java.lang.reflect.InvocationTargetException 
jenkins        | java.lang.reflect.InvocationTargetException

[mawinter69]

Just updated the plugin, looks I cannot add anymore system message (via JCasC or UI)

jenkins        |        at java.base/java.lang.Thread.run(Unknown Source)
jenkins        | Caused by: java.lang.NullPointerException: Cannot invoke "java.util.Set.removeIf(java.util.function.Predicate)" because the return value of "io.jenkins.plugins.customizable_header.UserHeader.getDismissedMessages()" is null
jenkins        |        at io.jenkins.plugins.customizable_header.CustomHeaderConfiguration.getSystemMessages(CustomHeaderConfiguration.java:143)
jenkins        |        at io.jenkins.plugins.customizable_header.headers.SystemMessageProvider.getSystemMessages(SystemMessageProvider.java:9)
jenkins        |        ... 154 more
jenkins        |  
jenkins        | [2024-06-03T13:34:06.103+0000] [WARNING] hudson.ExpressionFactory2$JexlExpression evaluate # Caught exception evaluating: instance[name] ?: attrs.default in /manage/appearance/. Reason: java.lang.reflect.InvocationTargetException 
jenkins        | java.lang.reflect.InvocationTargetException

Thanks for reporting, hopefully fixed in version 113.v09524a_dfd80d