Support for resource discovery

[mikestef9]

Is your feature request related to a problem?
Many AWS resources that can be provisioned by ACK require subnets and/or security groups as an input, such as RDS databases. However, organizations typically have VPC infrastructure managed by separate networking teams. This requires lots of coordination to pass around subnets IDs to ACK managed resources.

Describe the solution you'd like
The ability for ACK to discover resources that it doesn't manage (potentially via tags). This could be done by a separate controller (discovery-controller?) with a separate installation flow + documentation, and caveats & warnings about how this is not a true GitOps approach. But this would provide a good interim approach until all resources are managed through ACK.

Describe alternatives you've considered
We are working around by this copying subnets IDs from other places, and hardcoding into resources like SubnetGroup with RDS. However, this puts additional burden on developers, who ideally shouldn't care about subnets in this scenario.

[ack-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.
If this issue is safe to close now please do so with /close.
Provide feedback via https://github.com/aws-controllers-k8s/community.
/lifecycle stale

[a-hilaly]

/lifecycle frozen

[ack-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.
If this issue is safe to close now please do so with /close.
Provide feedback via https://github.com/aws-controllers-k8s/community.
/lifecycle rotten

[a-hilaly]

/lifecycle frozen