[C++] Use FetchContent for bundled opentelemetry

[raulcd]

Describe the enhancement requested

In order to reduce complexity of our ThirdParty dependency system we would like to keep reducing manual target definitions for our third party dependencies. In order to do so we could move opentelemetry from External Project to FetchContent.

• [C++] Refactor bundled dependencies from ExternalProject to FetchContent #45303

This issue is to track specifically moving opentelemetry. We should be able to remove nlohmann-json double installation once migrated.

This follows a similar approach to what a different PR was doing with abseil, c-ares, RE2, Protobuf, gRPC

• [C++] Use FetchContent for bundled Abseil #48074
• [C++] Use FetchContent for bundled c-ares #48091
• [C++] Use FetchContent for bundled RE2 #48178
• [C++] Use FetchContent for bundled Protobuf #48181
• [C++] Use FetchContent for bundled gRPC #48248

Component(s)

C++

[kou]

Issue resolved by pull request 48556
#48556