[C++] Use FetchContent for bundled Protobuf

[raulcd]

Describe the enhancement requested

Upgrading some dependencies has been quite challenging for the project like abseil / grpc / protobuf:

• [C++] Update bundled Abseil and gRPC #45063

There has been several attempts and the amount of work is massive because all of them are entangled and upgrading one requires to bump others.

When we upgraded to minimum CMake 3.25 the idea was to migrate our dependency management to FetchContent so we don't have to manually maintain and declare the different targets so those are generated at configure time.

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

This issue is to track specifically moving Protobuf to FetchContent as a new step before moving grpc.

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

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

This is only for moving the dependency to FetchContent, upgrading the dependency can be done afterwards as a separate issue.

We will be able to reduce the installation once we have moved gRPC.

Component(s)

C++

[raulcd]

Issue resolved by pull request 48183
#48183