[Doc] C++ client's doc is poor

[BewareMyPower]

Is your enhancement request related to a problem? Please describe.
The C++ client's doc is poor, a lot of interfaces are not well documented. For example, a lot of setters/getters have no document, see http://pulsar.apache.org/api/cpp/2.7.0-SNAPSHOT/classpulsar_1_1_producer_configuration.html for example. Users cannot get some default config values and its definition.

Describe the solution you'd like
Improve the documents. At least we should add documents for those interfaces.

Additional context
I'm working on new API of Producer::send recently (see #9176), when the PR is pushed, it can be treated as an example.

[BewareMyPower]

As the generated docs in my local environment, here's an example from #9287

As we can see, we can link ProducerConfiguration's related methods from Producer#send. However it requires these external methods have JavaDoc style comments. If not, these methods cannot be linked, like the current C++ API website:

The methods with dark bold text are not documented and have no link.

[Anonymitaet]

Hi @BewareMyPower I've added descriptions (suggestion mode) for the methods in the ProducerConfiguration.h, could you please help review?

https://docs.google.com/document/d/1SjO8SCVcbCMuEVW-HI1kf_jJjy-Ej5yFZoY9g4jUAQQ/edit

Feedback before 3/5 is highly appreciated, thanks.

[Anonymitaet]

Hi @BewareMyPower, I've added descriptions for the methods in the following files:

• ClientConfiguration.h
• ConsumerConfiguration.h
• ReaderConfiguration.h

Could you please help review?

Feedback before 3/31 is highly appreciated, thanks!

[BewareMyPower]

@Anonymitaet OK

[Anonymitaet]

@BewareMyPower I've added more descriptions for various classes in C++ client API - 0408 and C++ client API - 0409

Could you please review and give feedback before 4/13? Many thanks!

[BewareMyPower]

@Anonymitaet OK, I'm a little busy these days and may give some feedbacks on 4/11 or 4/12.

[Anonymitaet]

@BewareMyPower OK, take your time and thanks for your help.