Implement policy record tree building

[t-ionut]

• [x] regenerate tree on: IP changes, new record creation
• [x] add bounds on weights when the IP is the last one in the group
• [x] add health-checks per IP in AWS
• [x] organize tree as: each domain has a set of geo zones, each zone has a set of IPs
• [x] batch the tree operations (due to AWS limitations)
• [ ] on tree changes, duplicate then switch (not needed)
• [x] all operations should be done async
• [x] treat lock situations as atomic operations