Add missing include folders for example OTLP exporter

[ThomsonTan]

Added missing included folders and also renamed library target foo_library to otlp_foo_library in CMakeLists.txt. The name foo_library conflicts with the library in simple example.

gRPC dependency is still missing so I didn't add this exporter to the parent CMakeLists.txt, will fix it later.

[linux-foundation-easycla]

• ❌The commit (01b509a) is missing the User's ID, preventing the EasyCLA check. Consult GitHub Help to resolve. For further assistance with EasyCLA, please submit a support request ticket.

[codecov]

Codecov Report

Merging #300 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #300   +/-   ##
=======================================
  Coverage   94.55%   94.55%           
=======================================
  Files         146      146           
  Lines        6610     6610           
=======================================
  Hits         6250     6250           
  Misses        360      360           

[ThomsonTan]

Will fix user Id and resend this PR.