[CI] Upgrade Prometheus CI to opentelemetry-cpp 1.15.0

[marcalff]

Fix #432

Changes

• CI CMake Build, upgraded opentelemetry-cpp to 1.15.0
• CI Bazel build, upgraded opentelemetry-cpp to 1.15.0
• CI Bazel build, upgraded prometheus-cpp to 1.2.4
• Fixed a build warning, PrometheusPushExporterOptions::port is a string
• Fixed a crashing bug in unit tests in CreateSumPointData():
  • local variable instrumentation_scope is a unique_ptr
  • instrumentation_scope.get() is used to build the test data
  • instrumentation_scope goes out of scope, deleting the underlying pointer
  • the simulated data points to stale memory, leading to a crash when using instrumentation_scope
  • This happens with recent opentelemetry-cpp, where the prometheus exporter uses the scope
• Adjusted unit test CollectionNotEnoughSpace:
  • The prometheus exporter now exports the scope, as well as data
  • This increases the amount of data collected