Update KB page building MariaDB on CentOS

The page Building MariaDB on CentOS is missing couple of important things:

• Add wget as dependency
• By default cmake version installed from yum base repo is 2.8 that is not supported for MariaDB server to be built, we need version 3.1+. This fact is introduced in 2018 with commit d9613b750c6d.
  Task: Add instruction for cmake latest to be built:

  $ yum remove cmake

  $ wget https://github.com/Kitware/CMake/releases/download/v3.26.3/cmake-3.26.3.tar.gz

  $ tar zxvf cmake-3.*

  $ cd cmake-3.*

  $ ./bootstrap --prefix=/usr/local

  $ make -j$(nproc)

  $ make install

  $ yum remove cmake # removes 2.8

  $ ln -s /usr/local/bin/cmake /usr/bin/cmake # make symbolic link

  $ ln -s /usr/local/bin/cpack /usr/bin/cpack

• Based on MDEV-16758 we need to have source directory as well as build directory longer than default path determined with CPACK_RPM_BUILD_SOURCE_DIRS_PREFIX with default path: /usr/src/debug/${CPACK_PACKAGE_FILE_NAME}<component>, with while testing I found as /usr/src/debug/MariaDB/<source_path>.
  Task: Indicate to user to create build directory as well as source directory (like in case of containers to map volume) to longer path than default 25 characters.

  $ mkdir <my_long_path_source_directory> # this may be a volume on container

  $ mkdir <my_long_path_build_directory>

• Use -j($nproc} for make package