feat: (IAC-897) Annotate NGINX to indicate the desired subnets to provision LBs internal IP addrs from

[dhoucgitter]

Github format

Changes

• Add documentation for the added AWS specific configuration variable V4_CFG_AWS_LB_SUBNETS
• The V4_CFG_AWS_LB_SUBNETS values specifies the AWS subnets and by association the AWS availability zones to deploy the load balancing service to. Specifying a subnet value or values for this variable supercedes the Subnet Discovery method decribed in AWS docs and eliminates the need to tag subnets as described in scenario 2 of this table

Tests

Scenario	Provider	method	kubernetes_version	cluster_api_mode	V4_CFG_AWS_LB_SUBNETS	notes
1	AWS	Ansible	1.27	public	unset	AWS NLB AZs correspond to public tagged subnets via Subnet Discovery
2	AWS	Ansible	1.27	public	"subnet-034f8eaf7b0c8a744"	AWS NLB shows AZ was set to us-west-1a and it's private IP address is assigned from CIDR 192.168.130.32/28 which is the CIDR for subnet-033f8eaf7b0c8a744
3	AWS	Ansible	1.27	public	"subnet-033f8eaf7b0c8a744, subnet-0c20ecd67feefbee7"	AWS NLB shows AZs set to us-west-1a and us-west-1c and it's private IP address is assigned from CIDR 192.168.130.32/28 and CIDR 192.168.130.48/28 which are the CIDRs for subnet-033f8eaf7b0c8a744 and subnet-0c20ecd67feefbee7 respectively
4	AWS	Ansible	1.27	private, Environment setup using gitlab aws byo private-cluster.tfvars	unset	AWS NLB chooses AZs us-west-1c and us-west-1a from the public and private subnets. This is existing behavior and is not influenced by the new config variable.
5	AWS	Ansible	1.27	private, Environment setup using gitlab aws byo private-cluster.tfvars	subnet-04bbcb82452df7259	AWS NLB chooses AZ us-west-1a from the specified subnet-04bbcb82452df7259.
6	AWS	Ansible	1.27	private, Environment setup using gitlab aws byo private-cluster.tfvars	subnet-0efe7b1a630e947f3, subnet-013a0823b2666d44d	AWS NLB chooses AZs us-west-1c and us-west-1a and it's private IP address is assigned from CIDR 10.10.128.128/25 and 10.10.128.0/25 which are the CIDRs for subnet-0efe7b1a630e947f3 and subnet-013a0823b2666d44d respectively

[thpang]

LGTM