THRIFT-5668: Install FindLibevent.cmake (#2726)

Client: cpp

ThriftConfig.cmake uses our FindLibevent.cmake but "make install"
doesn't install FindLibevent.cmake. It causes an error with
find_package(Thrift) like the following:

    -- Found thrift: /tmp/xxx/tmp/local
    -- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.13")
    -- Found OpenSSL: /usr/lib/x86_64-linux-gnu/libcrypto.so (found version "3.0.7")
    CMake Warning at /usr/share/cmake-3.24/Modules/CMakeFindDependencyMacro.cmake:47 (find_package):
      By not providing "FindLibevent.cmake" in CMAKE_MODULE_PATH this project has
      asked CMake to find a package configuration file provided by "Libevent",
      but CMake did not find one.

      Could not find a package configuration file provided by "Libevent" with any
      of the following names:

        LibeventConfig.cmake
        libevent-config.cmake

      Add the installation prefix of "Libevent" to CMAKE_PREFIX_PATH or set
      "Libevent_DIR" to a directory containing one of the above files.  If
      "Libevent" provides a separate development package or SDK, be sure it has
      been installed.
    Call Stack (most recent call first):
      /tmp/xxx/tmp/local/lib/cmake/thrift/ThriftConfig.cmake:93 (find_dependency)

0 files changed, 0 insertions, 0 deletions