Update protos and remove targetOriginator

[mkysel]

Remove TargetOriginator field from AuthenticatedData structure and update protobuf definitions to use main branch

• Removes the TargetOriginator field from the AuthenticatedData structure in pkg/proto/xmtpv4/envelopes/envelopes.pb.go, eliminating explicit originator targeting for message routing
• Updates the protobuf generation script in dev/gen/protos to use the main branch instead of a specific feature branch
• Modifies the payer service in pkg/api/payer/service.go to remove backwards compatibility code for TargetOriginator and simplifies blockchain routing logic to only check IsCommit flag
• Removes test function TestMismatchingAADOriginatorOnPublishNoLongerFails and updates multiple test files to remove TargetOriginator field usage
• Adds new backup element types for events and welcome message encryption algorithm fields to various protobuf definitions

📍Where to Start

Start with the AuthenticatedData structure in pkg/proto/xmtpv4/envelopes/envelopes.pb.go to see the removal of the TargetOriginator field, then review the payer service changes in pkg/api/payer/service.go.

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Macroscope summarized 36d6d29.

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