[CMAKE] Set the project version through the cmake project macro

[dbarker]

The cmake project macro takes VERSION and LANGUAGE args which are not currently being set in otel-cpp CMakeLists.txt.

CMake uses the VERSION arg to set internal variables (See https://cmake.org/cmake/help/v3.31/command/project.html#options) which are used by CMake. One example is for providing more info to the user when they call find_package(opentelemetry-cpp CONFIG).

Previous cmake message when calling find_package(opentelemetry-cpp CONFIG)

-- Found opentelemetry-cpp: /usr/local/include  

New cmake message when calling find_package(opentelemetry-cpp CONFIG)

-- Found opentelemetry-cpp: /usr/local/lib/cmake/opentelemetry-cpp/opentelemetry-cpp-config.cmake (found version "1.22.0") 

Changes

• Move reading the api version header and setting the OPENTELEMETRY_VERSION and OPENTELEMETRY_ABI_VERSION_NO variables to cmake/version.cmake
• Set the VERSION and LANGUAGE args in project(opentelemetry-cpp ...)
• Set the OPENTELEMETRY_VERSION and OPENTELEMETRY_ABI_VERSION_NO as cached variables so users building otel-cpp in-tree with their project can know what version and abi number has been built.
• Add checks in the FetchContent CI test for the cached variables.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	fe8ce0c
🔍 Latest deploy log	https://app.netlify.com/projects/opentelemetry-cpp-api-docs/deploys/68a8fbd466df7c000868a51e

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.03%. Comparing base (dfa7118) to head (e249482).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3605   +/-   ##
=======================================
  Coverage   90.03%   90.03%           
=======================================
  Files         220      220           
  Lines        7069     7069           
=======================================
  Hits         6364     6364           
  Misses        705      705           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[marcalff]

Thanks for the fix.

See comments, with some simplifications.

[marcalff]

LGTM, thanks for the fix.