jaeger, build/op: add jaeger and it's dependencies as submodules

jaeger, build/op: add jaeger and it's dependencies as submodules

* This commit introduces Jaegertracing library as package libjaeger,
  pickwhich would be consumed by other ceph pacakges such as ceph-common0

* adds the following dependencies, which would be build from source
  using ExternalProjectHelper.cmake +IncludeJaeger.cmake +
  Build<package>.cmake scripts:

  jaegertracing: v0.6.0 [added as a submodule]
  opentracing: v1.6.0 [added as a submodule]
  thrift: 0.13.0 [added as a submodule]
  yaml-cpp: 0.6.0
  json(optional)

* updates Boost to be installed instead of being build only, because
  jaegertracing them during their build process.

* ceph.spec.in: introduces a default enabled jaeger packaging option,
  which could be disabled using --without-jaeger flag during rpmbuild

* note: libjaeger package if enabled will be a dependency on ceph-common, ceph-mon, rgw_common and transitively will be a dependency for modules that have them as  a dependency.

Signed-off-by: Deepika Upadhyay <dupadhya@redhat.com>