[C++][Documentation] Note caveats of a combined gRPC/Flight server

[asfimport]

See this GitHub issue: when building a combined gRPC/Flight service, care must be taken not to link gRPC twice on accident. This is noted briefly in the docstring but we should be more detailed and perhaps add prose documentation. We should also note this in the example.

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #11698
• apache/arrow-cookbook#106

_{Note: This issue was originally created as ARROW-14662. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Also see the related Cookbook issue.

[asfimport]

David Li / @lidavidm:
Looking at the Ubuntu 20.04 package:

• Ubuntu ships gRPC 1.3 (yikes!) so we build gRPC from source.

• We can't/don't want to distribute libgrpc++.so, so we link gRPC statically.

• We include gRPC and Protobuf in libarrow_bundled_dependencies.a

  So we should note that applications expecting to use solely Arrow Flight, but not Protobuf or gRPC, can use either the dynamic or static libraries, but applications that may include either Protobuf or gRPC must (1) use the static libraries and (2) use the same version of Protobuf as Arrow. That's rather a pain and it may be easier to just build Arrow from source…

[asfimport]

Yibo Cai / @cyb70289:
Issue resolved by pull request 11698
#11698