Specify OPENTELEMETRY_ABI_VERSION_NO with Bazel

[BYVoid]

Is your feature request related to a problem?
OPENTELEMETRY_ABI_VERSION_NO is by default 1 in Bazel, and there is no where to configure it, unlike CMake (WITH_ABI_VERSION_2).

Describe the solution you'd like
Consider adding a Bazel flag to allow changing OPENTELEMETRY_ABI_VERSION_NO as in https://github.com/open-telemetry/opentelemetry-cpp/blob/main/api/BUILD.

Describe alternatives you've considered
I tried to patch the Bazel build files.

[BYVoid]

Thanks for merging.

Would you consider setting the default abi_version_no to 2 in Bazel? As Bazel is hermetic (all deps are built from source), there is no ABI compatibility issue at all. It makes sense to allow users to use the latest APIs guarded by #if OPENTELEMETRY_ABI_VERSION_NO >=2 by default.

If this makes sense, I am happy to create another pull request.

[marcalff]

Moving to OPENTELEMETRY_ABI_VERSION_NO = 2 will cause breaking changes.

For example, see how parameters for opentelemetry::trace::TracerProvider::GetTracer() changed.

Users should be asking explicitly for abi 2 instead if they want to use it, we can not ship it by default for now.

Beside, ABI v2 can change without notice with more breaking changes, it is not stable yet.