feat: support custom subnet ID (--vnet-subnet-id)

[Bryce-Soghigian]

Fixes #199

Description
This pr solves the issue linked above and allows karpenter to tap into a specifed custom vnet + subnet id, via --vnet-subnet-id global flag. Both self-hosted and NAP deployments are expected to populate this from custom subnet specified for the cluster, which can be looked up from the system nodepool.

How was this change tested?

• ran make az-all-custom-subnet with new custom vnet cluster create:
• ran make az-perftest100 took 3 minutes to create all 100 nodes, they all join the subnet fine

Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: #
• No

Release Note

Support custom subnet ID via `--vnet-subnet-id` flag

[coveralls]

Pull Request Test Coverage Report for Build 8577118060

Details

• 76 of 82 (92.68%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 97.761%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/providers/launchtemplate/launchtemplate.go	28	34	82.35%

Totals
Change from base Build 8575878262:	0.04%
Covered Lines:	35672
Relevant Lines:	36489

---

💛 - Coveralls

[Bryce-Soghigian]

/test

[tallaxes]

Here is another place where subnet id is used (currently hardcoded, would need to change):

karpenter-provider-azure/pkg/providers/imagefamily/bootstrap/aksbootstrap.go

Line 298 in 0369403

Subnet: "aks-subnet", // xd

Now, I strongly suspect that on the node this affects only azure.json, and I can't think of why this would actually be needed. If this is indeed unused, it (quite possibly with some other fields) would be a prime candidate for removing from the contract. (This is very much related to contract discussion here Azure/AgentBaker#4208 (comment), cc @lilypan26)

[Bryce-Soghigian]

Here is another place where subnet id is used (currently hardcoded, would need to change):

Fixed this

[Bryce-Soghigian]

/test

[Bryce-Soghigian]

As a result of moving most of the refactoring into this pr, the subnet per nodeclass pr became much smaller: #243

[tallaxes]

Left some comments. The main thing is likely re using options rather than client config for subnet id (apologies for not catching this earlier)

[tallaxes]

BTW, where did the creation of cluster with custom subnet go? Or az-all-custom-subnet (mentioned in description)?

[Bryce-Soghigian]

BTW, where did the creation of cluster with custom subnet go? Or az-all-custom-subnet (mentioned in description)?

I screwed up the rebase maybe idk where it went

[Bryce-Soghigian]

/test

[Bryce-Soghigian]

/test

[tallaxes]

LGTM, pending test success. Thanks for all the fixes!

[tallaxes]

Approved, conditional on passing tests

[tallaxes]

/test

[tallaxes]

Further testing showed some custom VNet related targets have issues, fixing in #148 (as it changes the flow anyway ...)