feat(job-exec): add support of Direct VPC egress

[tanguynicolas]

Reissue due to a mistake on my part. It seems that not everyone followed the contributor's guide, which introduced changes to other components that I did not want to modify (there was some drift).

Hello,

Two PRs already exist, but seem to have been abandoned by their authors (https://github.com/GoogleCloudPlatform/terraform-google-cloud-run/pull/314 & https://github.com/GoogleCloudPlatform/terraform-google-cloud-run/pull/320).

The purpose of this PR is to activate this functionality, which has been available for several months now, for the “job-exec” submodule.

Thanks

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