What does this PR do?

Type of change: CICD infra improvement

• All example tests will now be run before PR can be merged (onnx_ptq-bash still in gitlab as it needs internal scratch space models. llm_eval / llm_autodeploy only run nightly to save per-PR gpu resource)
• Users can also manually trigger specific test fromhttps://github.com/NVIDIA/TensorRT-Model-Optimizer/actions/workflows/example_tests.yml
• We no longer need to depend on internal gitlab infra for tests (except nemo-megatron integration tests)

Testing

• Tests run in PR and manually via workflow_dispatch

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• Make sure you read and followContributor guidelines and your commits are signed.
• Is this change backward compatible?: Yes
• Did you write any new necessary tests?: No
• Did you add or update any necessary documentation?: No
• Did you updateChangelog?: No