Improve MQTT support

[andreniggemann]

Bugfixes:

• The change in ConnectingToBrokerState prevents an application crash that were not uncommon during debugging

Cleanup:

• Mostly typos in the string resources or non equal punctuation
• Don't use the obsolete Payload Method and use ReadOnlySequence instead. To avoid unnecessary array copies methods deserializing the data have breaking signature changes
• Remove Newtonoft.Json in favor of System.Text.Json

Features:

• Add the option to add custom topics as the User by removing internal access modifiers from MqttTopic Serialize and Deserialize
• Add Retain information for Publishing and Receiving messages
• Support Mqtt5 response topics
• Support unsubscribing from Topics, by removing or changing the resource
• Support changing the broker without restarting the Resource Management, by a) providing a Reconnect method and b) handling changes to the relevant properties
• Support diagnostic tracing of message contents, before and after deserialization

[dbeuchler]

• Missing summaries in public members
• Several one-liners, bad readability of long lines. Separate them
• Title of pull request

[1nf0rmagician]

You already mentioned that there are breaking changes in here, would you put them in the migration guide please? 🙂

[1nf0rmagician]

would you put these properties next to the other props?

[1nf0rmagician]

Do you want to remember the operation id here to cancel it in the OnStop of the driver?

[andreniggemann]

I know included this in a slightly modified form.
I placed it in OnDisconnect which is called by OnStop. This has the benefit that it should also work for other situations where a disconnect is requested.