Control-plane/data-plane refactoring

[purplefox]

This is a super task to outline tasks required in refactoring Tektite to split out control plane:

Concensus and basics of controller:

• S3 based concensus
• group membership

Then we try and get produce path working:

• Stream and topic metadata managed in controller
• Move lsm manager - LSM metadata and compaction into controller
• Implement offsets management in controller
• Implement basic agent with produce, and buffering

Then get consume path working:

• Move group controller to level manager
• Implement fetch in tekagent
• Implement fetch cache

Other bits:

• Move credentials management into controller