Support building with the default apt sources on Ubuntu 20.04

[BewareMyPower]

Motivation

Currently the Python client cannot be built with the default apt sources on Ubuntu 20.04, whose default CMake version is 3.16. However, even after I installed CMake 3.24 on Ubuntu 20.04, CMake would still fail to find Boost.Python.

Modifications

To fix the Boost.Python not found issue, find the Python component instead of Python3 when finding Boost.

In addition, when finding Python3, find the Development component instead of the Development.Module, which is a sub-component of Development. See
https://cmake.org/cmake/help/latest/module/FindPython3.html.

After that, the minimum required CMake version becomes back to 3.12 from 3.18, which was upgraded in
#11.

[BewareMyPower]

The CMake error is:

CMake Error at /usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0/BoostConfig.cmake:117 (find_package):
  Could not find a package configuration file provided by "boost_python3"
  (requested version 1.71.0) with any of the following names:

    boost_python3Config.cmake
    boost_python3-config.cmake

  Add the installation prefix of "boost_python3" to CMAKE_PREFIX_PATH or set
  "boost_python3_DIR" to a directory containing one of the above files.  If
  "boost_python3" provides a separate development package or SDK, be sure it
  has been installed.
Call Stack (most recent call first):
  /usr/lib/x86_64-linux-gnu/cmake/Boost-1.71.0/BoostConfig.cmake:182 (boost_find_component)
  /home/xyz/cmake-3.24.2-linux-x86_64/share/cmake-3.24/Modules/FindBoost.cmake:594 (find_package)
  CMakeLists.txt:48 (find_package)

or the following messages with -DBoost_NO_BOOST_CMAKE=ON option:

CMake Error at /home/xyz/cmake-3.24.2-linux-x86_64/share/cmake-3.24/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find Boost (missing: python3) (found version "1.71.0")
Call Stack (most recent call first):
  /home/xyz/cmake-3.24.2-linux-x86_64/share/cmake-3.24/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
  /home/xyz/cmake-3.24.2-linux-x86_64/share/cmake-3.24/Modules/FindBoost.cmake:2376 (find_package_handle_standard_args)
  CMakeLists.txt:48 (find_package)

[BewareMyPower]

It can be fixed by a simple CMake upgrade now after #23.

We cannot use find_package(Python3 COMPONENTS Development) because it will fail in manylinux container.