Integrates the new features of the the Kokoro PSM Interop install library introduced in grpc/psm-interop#73.

Nearly all common functionality was moved from per-language/per-branch PSM Interop build scripts to [psm_interop_kokoro_lib.sh](https://github.com/grpc/psm-interop/blob/main/.kokoro/psm_interop_kokoro_lib.sh):
1. The list of tests in the each test suite
2. Per-test-suite flag customization
3. `run_test` methods
4. `build_docker_images_if_needed` methods
5. Generic `build_test_app_docker_images` methods (simple docker build + docker push + docker tag). grpc-java is one exception, as it doesn't run docker directly, but a cloudbuild flow.

Now all PSM Interop jobs share the same buildscripts by all test suites:
1.  buildscript that invokes the test: `psm-interop-test-{language}.sh` (configured as `build_file` in the build cfg)
2. buildscript that builds the xDS test client/server and publishes them as a Docker image: `psm-interop-build-{language}.sh` (conventional name called from `psm_interop_kokoro_lib.sh`)

`psm-interop-test-{language}.sh`:
1. Sets `GRPC_LANGUAGE`, `BUILD_SCRIPT_DIR` environment variables.
2. Downloads the shared `psm_interop_kokoro_lib.sh` from the main branch of the psm-interop repo.
3. Sources `psm-interop-build-{language}.sh`
4. Calls `psm::run "${PSM_TEST_SUITE}"` (`PSM_TEST_SUITE` configured in the cfg file).

`psm-interop-build-{language}.sh`:
1. Defines `psm::lang::build_docker_images` which is called from `psm_interop_kokoro_lib.sh`.
2. Invokes any repo-specific logic.
3. May use `psm::build::docker_images_generic` for generic Docker build, tag, push, or provide implement its own build/publish method.

References:
- b/288578634
- See the full list of the new features at grpc/psm-interop#73.
- Additional fixes to the shared lib: grpc/psm-interop#78, grpc/psm-interop#79

Closes grpc#36450

COPYBARA_INTEGRATE_REVIEW=grpc#36450 from sergiitk:psm-interop-common-prod-tests 4b977b7
PiperOrigin-RevId: 630502807