chore: remove build artifacts from git, add to .gitignore

Untrack all binaries (build/, tests/e2e-grpc/build/, build_info, *.so).
These are build outputs that should never be committed.

Author: xaionaro@dx.center

.gitignore

@@ -1,2 +1,6 @@
+/build/
+/tests/e2e-grpc/build/
+/build_info
+*.so
 cover.out
 examples/test_results/