[improve][doc] Simplify the Install section and promote a top-level "Installation" title

[tisonkun]

Fixes #17385

Documentation

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[tisonkun]

cc @BewareMyPower @shibd @RobertIndie

[tisonkun]

Previews:

[tisonkun]

@merlimat @Anonymitaet Thanks for your reviews! Comments addressed.

[BewareMyPower]

I have a concern that should we just link to https://github.com/apache/pulsar/tree/master/pulsar-client-cpp#compilation instead of adding repeated documents here?

Building C++ client from source is usually not easy for users other than experienced C++ developers. The content is a little complicated for basic users. They need to know:

• The dependencies
• How to install them
• The requirements of the C++ compiler and CMake

And the details are all covered by https://github.com/apache/pulsar/tree/master/pulsar-client-cpp#readme

For example, I see you added -DBUILD_TESTS=OFF options. However, it's already covered in here, from which you can see other options like using DBUILD_PYTHON_WRAPPER=OFF to skip building python client.

Showing a simplified document might make those C++ users (not deep developers) confused and they might ask why cannot they build successfully after following the guide in the official website.

[tisonkun]

I have a concern that should we just link to https://github.com/apache/pulsar/tree/master/pulsar-client-cpp#compilation instead of adding repeated documents here?

I agree that build from source has low frequency and users who want to do it will be OK to jump to the source code repository. Will push a commit tomorrow. Also, cc @merlimat @RobertIndie @shibd for inputs.

[tisonkun]

@shibd @Demogorgon314 updated. Here is the preview:

[tisonkun]

@BewareMyPower @Demogorgon314 @RobertIndie It seems we reached a consensus here. Could you help with merging this PR?