feat: add dropped table ddl tasks

[v0y4g3r]

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Refer to a related PR or issue link (optional)

• Supports GreptimeDB soft-drop table recovery work: feat: add soft-drop table recovery procedures greptimedb#8061

What's changed and what's your intention?

This PR extends the metasrv protobuf DDL task API for dropped-table lifecycle operations.

• Adds UndropTableTask to greptime.v1.meta.DdlTaskRequest with direct catalog_name, schema_name, table_name, and required table_id fields.
• Adds PurgeDroppedTableTask to greptime.v1.meta.DdlTaskRequest with direct catalog_name, schema_name, table_name, and optional table_id fields.
• Extends DdlTaskRequest.task with undrop_table_task tag 19 and purge_dropped_table_task tag 20.
• Regenerates Rust, Go, Java, and C++ bindings plus the checked-in descriptor blob.

Compatibility notes:

• Existing tags and message fields are not renumbered or removed.
• The new oneof variants use previously unused tags 19 and 20.
• These are metasrv procedure-submission tasks, so the fields are kept directly on the task messages instead of adding client-facing greptime.v1.DdlRequest expressions.

Checklist

• I have written the necessary comments.
• I have added the necessary unit tests and integration tests.

[Copilot]

Pull request overview

This PR extends the greptime.v1.meta.DdlTaskRequest protobuf API with two new DDL task variants to support workflows around dropped tables (restoring a dropped table and purging dropped-table metadata/data), and regenerates the Rust/Java/C++ bindings accordingly.

Changes:

• Add UndropTableTask and PurgeDroppedTableTask message types to proto/greptime/v1/meta/ddl.proto.
• Extend DdlTaskRequest.task oneof with undrop_table_task (tag 19) and purge_dropped_table_task (tag 20).
• Regenerate Rust (prost), Java, and C++ protobuf outputs to include the new message types and oneof variants.

Reviewed changes

Copilot reviewed 3 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
proto/greptime/v1/meta/ddl.proto	Defines the new task messages and wires them into DdlTaskRequest’s oneof.
src/generated/greptime.v1.meta.rs	Updates Rust generated structs and oneof enum to include the new tasks.
java/src/main/java/greptime/v1/meta/Ddl.java	Updates Java generated protobuf classes for the new messages/oneof cases.
c++/greptime/v1/meta/ddl.pb.h	Updates C++ generated headers for new message types and oneof accessors.
c++/greptime/v1/meta/ddl.pb.cc	Updates C++ generated implementation (descriptors, parsing/serialization, etc.).

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