Add restate.dev

[gvdongen]

Restate (https://restate.dev/) is a durable runtime for agents and backends. It provides durable execution, durable RPC/messaging, stateful objects, and concurrency control.

Type of change

• [x ] Add an entry to an existing category.
• Remove an existing entry. Provide rationale
• Modify an existing entry. Provide rationale
• Add/modify/remove a category or subcategory. Provide rationale
• Other fixes or amendments.

Rationale

Checklist

• [x ] The contribution follows the CONTRIBUTING.md document guidelines.

Regarding the suggested entry:

• [ x] It is sorted alphabetically in its section.
• [x ] It does not exist already in the list.
• [ x] It is not for marketing purposes.