[INSTALL] add cmake components to the package

[dbarker]

Fixes #3218

Overview

This PR introduces CMake COMPONENTS to the opentelemetry-cpp package. Components are essentially named groups of CMake targets and can be passed to the find_package function to more selectively include targets and dependencies.

For example, with this PR the following will only include the opentelemetry-cpp::api header only target and search for no other dependencies that may be needed by other targets of the package.

# only find and include the api target
find_package(opentelemetry-cpp CONFIG REQUIRED COMPONENTS api)

Using components like this provides developers more control over what targets and dependencies CMake includes and should help reduce the scope of dependency issues a developer may encounter when building their instrumented CMake projects against different versions/configurations of the installed opentelemetry-cpp package.

Please see the updated INSTALL.md file of this PR for the proposed components to targets mapping.

Backwards compatibility is covered by including all components and finding all dependencies when the developer does not pass any components to find_package as in the case below.

# include all targets and find all dependencies of the package
find_package(opentelemetry-cpp CONFIG REQUIRED)

Changes

1. Breaks up the single opentelemetry-cpp-target.cmake file into target files per component by updating the CMake install commands that create export sets in the CMakeLists.txt files for each of the targets.
2. Updates the opentelemetry-cpp-config.cmake to include a complete list of all components and all targets. This file now reacts to the opentelemetry-cpp_FIND_COMPONENTS list set by find_package when a developer adds the COMPONENTS arguments.
3. Updates the INSTALL.md file with the proposed components to targets mapping and guidance on usage.
4. TODO - add ci tests on the installed packages/components/targets.

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	80a3cb3
🔍 Latest deploy log	https://app.netlify.com/sites/opentelemetry-cpp-api-docs/deploys/676a0181f03f5a0008727e3a

[dbarker]

Posting this as draft and seeking feedback. Interested in thoughts/concerns on the general approach and the proposed component to target mapping.

If the proposed changes look reasonable, I'd be happy to add the ci tests to verify the changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.16%. Comparing base (4998eb1) to head (80a3cb3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3220   +/-   ##
=======================================
  Coverage   88.16%   88.16%           
=======================================
  Files         198      198           
  Lines        6224     6224           
=======================================
  Hits         5487     5487           
  Misses        737      737