[Feature] Support for whole database or multi table compaction

### Search before asking

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

### Motivation

When using the "write only=true" table attribute for multiple Paimon tasks, it will necessitate performing background compaction tasks. If Paimon can support compacting the entire database's files (all Paimon tables) or merging multiple tables in a single task, it would be something to anticipate!

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

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

No files, tests, or entry points are named. Start by locating the existing background compaction entry point, then determine how it could target all Paimon tables or multiple tables in one task; done means the requested whole-database or multi-table compaction behavior is implemented and covered by tests.

Written by the indexing model from the issue text.