Remove parent_model version suffix if passed to Vertex AI operators

[e-galan]

Check the parent_model parameter for model version suffix (looks like <model_id>@1 or <model_name>@1) and remove it from the parent_model string if it is present there. Keep the same value if the suffix is not present.

This is needed because sometimes operators can be passed with the parent_model value which contains such a suffix, for example when the user wants to extract a model id / model name from a serialized result of CreateCustomTrainingJobOperator run and then pass it to another operator as the parent_model. Vertex AI is not able to find a resource if it contains this suffix, and will return an error that will prevent the user from submitting a new training job.

This PR partially reverts #38417 which removed a similar functionality because it caused a bug in the cases when the parent_model did not contain any suffixes. This PR should cover both problems.

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[VladaZakharova]

Hi @eladkal !
Can we check this PR and include it to next google-provider release? Thanks!