Migrate Buf configuration files from v1 to v2

[mmorel-35]

Description

Migrate Buf configuration files from v1 to v2 following https://buf.build/docs/migration-guides/migrate-v2-config-files/

[istio-policy-bot]

😊 Welcome @mmorel-35! This is either your first contribution to the Istio api repo, or it's been
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[istio-testing]

Hi @mmorel-35. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[zirain]

/ok-to-test