642: Cross-Zone Load Balancing Management

[tlake]

What does this pull request do? Introduces a new feature to load balancers that allows configuration of cross-zone load balancing.

How should this be tested? Spin up a new Layer0 dev API and:

• use dev client to create load balancers both with and without the --disable-cross-zone flags
• use dev client to test usage of the new load balancer subcommand "cross-zone":
  • with no args to view
  • with --enable flag
  • with --disable flag
• use dev Terraform provider to test behavior of the load balancer's cross_zone field in a Terraform configuration:
  • omit the field
  • cross_zone = true
  • cross_zone = false

Checklist

• [x] Unit tests
• [x] Smoke tests (if applicable)
• ~[ ] System tests (if applicable)~
• [x] Documentation (if applicable)

closes #642

corresponding issue in JIRA: https://jiraims.rm.imshealth.com/browse/OCEMCM-5776

[sesh-kebab]

Nice work and the quick turn around time! @zpatrick would be impressed.

Initial pass over the code looks fine. But doing a more thorough review pass and QA your RC, will take a bit more time given the current workload. Just wanted to let you know this hasn't been forgotten about.