add new network peering fields

[danawillow]

Fixes hashicorp/terraform-provider-google#6266

Release Note Template for Downstream PRs (will be copied)

* added `export_subnet_routes_with_public_ip` and `import_subnet_routes_with_public_ip` to `google_compute_network_peering`

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 3 files changed, 81 insertions(+), 95 deletions(-))
Terraform Beta: Diff ( 3 files changed, 81 insertions(+), 95 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=119562"