Allow plugins to add CFN tags and outputs

[Luke-Humphreys]

What

Adding the ability for plugins to inject cloud formation tags into control plane and node pool stacks.
Adding the ability for plugins to inject output cloud formation into control plane, node pool, etcd and network stacks.

Why

In the process of developing a plugin for the cluster-autoscaler I noticed that you can only inject resources into cloud formation stacks from plugins, this meant I couldn't add the necessary ASG tags for the cluster-autoscaler. The functionality was already there, I just extended it a little bit.

[Luke-Humphreys]

/assign @redbaron

[Luke-Humphreys]

/assign @davidmccormick

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #1575 into master will increase coverage by <.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1575      +/-   ##
==========================================
+ Coverage    25.8%   25.81%   +<.01%     
==========================================
  Files          98       98              
  Lines        5057     5063       +6     
==========================================
+ Hits         1305     1307       +2     
- Misses       3605     3609       +4     
  Partials      147      147

Impacted Files	Coverage Δ
pkg/model/types.go	66.66% <ø> (ø)	⬆️
pkg/api/plugin.go	0% <ø> (ø)	⬆️
pkg/model/stack_new.go	32.33% <33.33%> (+0.03%)	⬆️

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[davidmccormick]

/lgtm

[davidmccormick]

Thanks @Luke-Humphreys for this useful expansion of our plugin functionality! 🙏