Eclipse Ditto 2.1.0

Eclipse Ditto 2.1.0 includes the following topics/enhancements:

• Support consuming messages from Apache Kafka -> completing the Apache Kafka integration as fully supported Ditto managed connection type
• Conditional requests (updates + retrievals)
• Enrichment of extra fields for ThingDeleted events
• Support for using (HTTP) URLs in Thing and Feature "definition" fields, e.g. linking to WoT (Web of Things) Thing Models
• HMAC based authentication for Ditto managed connections, see Blogpost
• SASL authentication for Azure IoT Hub
• Publishing of connection opened/closed announcements
• Addition of new "misconfigured" status category for managed connections indicating that e.g. credentials are wrong or connection to endpoint could not be established to to configuration problems
• Support "at least once" delivery for policy subject expiry announcements

The following notable fixes are included:

• Fix "search-persited" acknowledgement not working for thing deletion
• Fix reconnect loop to MQTT brokers when using separate MQTT publisher client 

The following non-functional work is also included:

• Support for tracing reporting traces to an "Open Telemetry" endpoint
• Improving cluster failover and coordinated shutdown + rolling updates
• Logging improvements, e.g. configuring a logstash server to send logs to or more options to configure a logging file appender
• Improving background deletion of dangling DB journal entries / snapshots based on the current MongoDB load
• Improving search update by applying "delta updates" saving lots of bandwith to MongoDB
• Reducing cluster communication for search updates using a smart cache