[Umbrella] Umbrella issue for System Tables

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.

### Motivation

This is an umbrella issue for system tables. The details is in [FIP-39](https://cwiki.apache.org/confluence/display/FLUSS/FIP-39%3A+System+Tables)

We are going to implement some specific system table or system views, to have a glance how system tables/views work, and check or verify whether the design is good enough for real cases.

We do it in three steps:
1. Construct the basic framework for system tables/views. Including components, interfaces, APIs... etc.
2. Implement a system view `sys.table_buckets`, to show the table bucket distributions, replicas and isr information.
3. Implement an internal system table `sys.consumer_offset`, with related offset management functionalities. With this case, we can check how fluss system table work.

### Solution

_No response_

### Anything else?

_No response_

### Willingness to contribute

- [ ] I'm willing to submit a PR!

Start by reading FIP-39, the design document linked in the issue, and compare its three proposed stages: the system table/view framework, sys.table_buckets, and sys.consumer_offset. No source files, tests, or implementation entry points are named, and completion is not defined beyond implementing those stages, so this umbrella issue needs to be split into concrete tasks first.

Written by the indexing model from the issue text.