Add Multi-Table Transaction API

### Proposed Change

Iceberg currently supports transactions at the table level via the [Transaction API](https://github.com/apache/iceberg/blob/master/api/src/main/java/org/apache/iceberg/Transaction.java), which allows one or more updates to a single table in an atomic manner. However, there is user demand in performing an all-or-nothing operation across multiple tables. This would enable more complex workflows that rely on updating multiple tables within a single transaction.

**Goals**
* necessary APIs that express and define working with transactions that allow atomic changes to multiple tables
* A base set of tests that could be used by other implementations
* one reference implementation with the RESTCatalog

**Non-Goals**
* Implementing multi-table TX support for other catalogs
* Only support for Iceberg tables will be added

### Proposal document

https://docs.google.com/document/d/1UxXifU8iqP_byaW4E2RuKZx1nobxmAvc5urVcWas1B8/edit
### Specifications

- [X] Table
- [ ] View
- [X] REST
- [ ] Puffin
- [ ] Encryption
- [ ] Other

Start by reading the linked proposal and the existing API in api/src/main/java/org/apache/iceberg/Transaction.java. Define the multi-table transaction APIs, add the base tests for other implementations, and provide the reference implementation for RESTCatalog. Done means atomic changes across multiple Iceberg tables are supported through the specified Table and REST scope.

Written by the indexing model from the issue text.