test: access control user story

Summary

• test: access control user story

Tested scenarios:

1. Alice is granted a privilege to create global/sharded table
2. Alice can create, read, and write it
3. Bob can't read it
4. Alice grants Bob a privilege to read it
5. Now Bob can read it, but he still can't write

Close #395 (closed) Supersedes !742 (closed)

Ensure that

• New code is covered by tests
• API is documented
• Changelog is up to date
• (if Lua API changed) Lua API version is bumped in luamod.rs
• (if necessary) A follow-up doc issue is created in picodata/docs and linked here