Add component metadata

[tylerhawkes]

Add component metadata and permissions proto definitions for MLS message contents

Adds a new protobuf file component_permissions.proto to the xmtp.mls.message_contents package defining three new types:

• ComponentType enum with six values covering bytes, TLS maps, and set types
• ComponentPermissions message with per-operation MetadataPolicy fields for insert, update, and delete
• ComponentMetadata message grouping a component's permissions and type

^{Macroscope summarized f0796a6.}

[macroscopeapp]

Approvability

Verdict: Approved

This PR adds a new proto file with type definitions for component metadata (enum and two messages). The changes are purely additive schema definitions with no runtime impact until consumers are implemented. The author is the designated code owner of the new file.

^{You can customize Macroscope's approvability policy. Learn more.}

[github-actions]

🎉 This PR is included in version 3.89.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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