[CMAKE] Clean up pkgconfig install methods and add tests

[dbarker]

Background:

This issue is to track work addressing #3829 (comment)

The opentelemetry_add_pkgconfig CMake function creates and installs pkgconfig files per CMake target.

Currently this method is invoked for each target with the target name, a description, and dependencies. The corresponding pkgconfig files are only superficially verified in CI and are not used to compile any tests or examples. Regressions in pkgconfig support can be easily missed.

The otel_add_component function creates the install components for the opentelemetry-cpp CMake package. This method can be updated to accept a description and to create the pkgconfig files for each target in the component.

Scope:

1. Add a description arg to otel_add_component
2. Add the pkgconfig file install functionality to otel_add_component
3. Add a CMake based pkgconfig test for the generated pkgconfig files against the install test files (./install/test/src)

[yigitcan-ozturk]

I'd like to work on this. I'll keep the scope to the three items described here: extend otel_add_component with the component description, move pkg-config generation/install into that helper, and add a CMake install/pkg-config test that compiles against the generated files. I'll preserve the current per-target dependency semantics and add focused coverage rather than broad CMake cleanup.