[improve][fn] Support subscriptionPosition and DLQ for Go instance

[jiangpengcheng]

Fixes #22445

Main Issue: #xyz

PIP: #xyz

Motivation

Modifications

Support subscriptionPosition and DLQ for Go instance

Verifying this change

• [x] Make sure that the change passes the CI checks.

• [x] This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• [ ] Dependencies (add or upgrade a dependency)
• [ ] The public API
• [ ] The schema
• [ ] The default values of configurations
• [ ] The threading model
• [ ] The binary protocol
• [ ] The REST endpoints
• [ ] The admin CLI options
• [ ] The metrics
• [ ] Anything that affects deployment

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

PR in forked repository: https://github.com/jiangpengcheng/pulsar/pull/32