Add tags for boost versions about boost-cmake

[bilke]

This would be really cool as it would help in using this repo with CPM. CPM uses the tags for versioning.

[freol35241]

@bilke

FYI, for use with CPM, I ended up doing the following (bypassing this repo since I only need header-only parts of boost anyway and to be able to update the version of boost when I want):

CPMAddPackage(
  NAME Boost
  VERSION 1.76.0
  URL https://boostorg.jfrog.io/artifactory/main/release/1.76.0/source/boost_1_76_0.tar.gz
  DOWNLOAD_ONLY True 
)
if(Boost_ADDED)
  # Define the header-only Boost target
  add_library(Boost::boost INTERFACE IMPORTED GLOBAL)
  target_include_directories(Boost::boost SYSTEM INTERFACE ${Boost_SOURCE_DIR})

  # Disable autolink
  target_compile_definitions(Boost::boost INTERFACE BOOST_ALL_NO_LIB=1)
endif()

target_link_libraries(<your_target> Boost::boost)

[iboB]

@freol35241 same here