Fix webhook create/list output to use protojson

[nikohofmann]

Fix buf beta registry webhook create and buf beta registry webhook list printing empty objects ({} / [{}]) instead of actual webhook data.

Root cause: both commands used encoding/json to marshal proto-generated structs. Proto structs store field data in unexported fields, invisible to encoding/json, so all fields silently serialize as zero values. Fix is to replace encoding/json.MarshalIndent with protojson.MarshalOptions{Multiline: true, Indent: "\t"}.Marshal, which uses the protobuf reflection API and correctly reads proto field values.

Note: the create output shape changes from a bare {...} to {"webhook": {...}} to match the RPC response structure.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 22, 2026, 4:19 PM

[doriable]

Looks good to me, thank you for putting this up! We also chatted about testing out this fix etc.

Stamping ahead of time, but do you mind adding a changelog statement for this, since this fixes a user-facing issue with webhooks? Thank you!