User Defined Network Segmentation Feature Gate

[tssurya]

What this PR does and why is it needed

• [x] Adds notion of "primary network" for secondary networks on the NAD
• [x] Adds enable-network-segmentation feature gate for this feature

Special notes for reviewers

This will be leveraged in future commits

How to verify it

UTs are added

Details to documentation updates

New config flag docs done!

Description for the changelog

Add feature gate for user-defined-networks-feature

Does this PR introduce a user-facing change?

Allows users to enable user-defined-networks via feature gate

[tssurya]

/assign @qinqon for reviews

[tssurya]

ah woops fixing the UT snafu

[coveralls]

coverage: 52.705% (-0.01%) from 52.716% when pulling 10382697de7736f6cb564bc190248835ddcc49cf on tssurya:user-defined-network-segmentation-feature-gate into 701b8e077c6d5639c45ad5cc41fbd4d8759ddc56 on ovn-org:master.

[coveralls]

coverage: 52.76% (+0.04%) from 52.716% when pulling 19afe52ff7a7f5869b520aff9280857d1f725bcc on tssurya:user-defined-network-segmentation-feature-gate into 701b8e077c6d5639c45ad5cc41fbd4d8759ddc56 on ovn-org:master.

[tssurya]

known failure:

[FAIL] e2e egress IP validation [OVN network] Using different methods to disable a node's availability for egress Should validate the egress IP functionality against remote hosts [It] disabling egress nodes impeding GRCP health check

https://github.com/ovn-org/ovn-kubernetes/actions/runs/9546389361/job/26310245921?pr=4446 ^ AND: https://github.com/ovn-org/ovn-kubernetes/issues/4447

unsure what exactly happened ^ this is new failure and has been happening quiet frequently now