Zeebe Simple Monitor 0.15.0

Changelog

• remove JDBC exporter and import records via Hazelcast
• show timer of workflow start event
• show message subscription of workflow message start event
• notify about updates of workflow
• replace payload input form by variable key-value form
• disable update variable if instance not running
• setup custom error page
• remove worker page
• migrate to Zeebe 0.20.0