Support for hosting extensions

[YAJeff]

With this change, the MQTTnet server can be hosted using Microsoft.Extensions.Hosting library, rather than full ASP.net core SDK.

[chkr1011]

In my opinion we should call this project "MQTTnet.Extensions.Hosting" to fit the other extensions (The Asp library was introduced before the naming pattern was established).

[chkr1011]

@YAJeff Ping?

[YAJeff]

Yes. Sorry. I have made those changes internally. Sorry. Been traveling for work. Will check in. There were other changes I've added to make things a little more solid/sound. Will have completed by the end of the weekend.

[chkr1011]

@YAJeff Please agree to the Contributor License. Then I will merge this PR.

[kallayj]

@dotnet-policy-service agree company="CARIAD Inc"

[kallayj]

@chkr1011 I've merged the latest from main into @YAJeff's fork and agreed to the CLA on behalf of the company we both work for.

[chkr1011]

@kallayj This does not seem to work. The agreement is still in "Contributor License Agreement is not agreed yet." state. I am afraid you have to create a new PR on your own (or please @YAJeff) to accept it.

[YAJeff]

@dotnet-policy-service agree company="CARIAD Inc"

[kallayj]

@chkr1011 the CLA check has passed, can this move forward?

[chkr1011]

@kallayj I applied the code style and moved the tests a little around to get the code compiling.

There are still some warnings left and some new properties are not even used. Please let me know when the code is finished so that I can review it.

[kallayj]

@chkr1011 I addressed the nullable reference type warnings. Where are you seeing unused properties?

[chkr1011]

Please see "MqttServerHostingOptions.WebSocketRoute". It is set but never read. Same for "WebSocketAuthenticationCallback".

[kallayj]

@chkr1011 I removed those properties.