Support query task progress for non-gremlin job

> E.g: some task like [rebuild-index](https://hugegraph.github.io/hugegraph-doc/clients/restful-api/rebuild.html) can take a long time.

We need a way to query the progress of these tasks like [this](https://hugegraph.github.io/hugegraph-doc/clients/restful-api/task.html)

Start with the linked rebuild-index and task REST API documentation to understand the existing task-progress behavior. Then identify how non-Gremlin long-running tasks should expose progress and what API contract is needed. Done means a task such as rebuild-index can be queried for progress, with corresponding tests or documentation showing the supported request and response.

Written by the indexing model from the issue text.