enhancement(greptimedb_logs): provide a default value for greptimedb logs pipeline_name

[sunng87]

Summary

The change made pipeline_name for greptimedb log sink an optional configuration item. A default value is provided.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Integration test provided

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• [] Please read our Vector contributor resources.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run dd-rust-license-tool write to regenerate the license inventory and commit the changes (if any). More details here.

References

[pront]

Thanks @sunng87