Simplify dependency upgrade process and upgrade Pulsar C++ client to 3.1.0

[BewareMyPower]

Motivation

Currently there are many files that require the download URLs of dependencies to download them. It's hard to maintain if some download URL changed. For example, https://github.com/apache/pulsar-client-python/pull/17 updates the ZLib download URL under https://zlib.net/fossils/ for macOS build. However, the ZLib download URL for Linux is under https://github.com/madler/zlib/archive/. The same goes for the Pulsar C++ client, it's hard to test another URL because the candidates and the official releases are stored in different paths.

Modifications

Add a dep-url.sh to provide two shell functions:

• pulsar_cpp_base_url: Print the base URL of the Pulsar C++ client release, there are the source code or binaries in the subpath.
• download_dependency: Download the source code according to the dependency file and the dependency name.

Then apply the dep-url.sh in all files that need to download the source or binary of the dependencies.

In addition, this PR upgrades the pulsar-cpp dependency to 3.1.0 so that the Windows build can depend on an official release.

[BewareMyPower]

Now, all tests passed. Wait for the official C++ client 3.1.0 release.

[BewareMyPower]

Let's merge it first. After the official 3.1.0 release is done, we only need to update the URL in build-support/dep-url.sh.