Adding tools to fetch external etcd cluster from EKS-A Controller

[maxdrib]

Issue #, if available: https://github.com/aws/eks-anywhere/issues/2260

Description of changes: This PR adds the functions for the EKS-A controller to reconcile upgrades and consider an external etcd cluster.

Testing (if applicable): Successfully scaled cluster with changes from https://github.com/aws/eks-anywhere/pull/2938, unit tests

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[eks-distro-bot]

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[codecov[bot]]

Codecov Report

Merging #3392 (bc86fe6) into main (308eca2) will increase coverage by 0.17%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3392      +/-   ##
==========================================
+ Coverage   64.73%   64.91%   +0.17%     
==========================================
  Files         352      352              
  Lines       28264    28387     +123     
==========================================
+ Hits        18298    18427     +129     
+ Misses       8654     8648       -6     
  Partials     1312     1312              

Impacted Files	Coverage Δ
pkg/controller/clusterapi.go	100.00% <100.00%> (ø)
pkg/controller/clusters/clusterapi.go	100.00% <100.00%> (ø)

... and 12 files with indirect coverage changes

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[jonathanmeier5]

As far as I'm aware this work is now being captured in the lifecycle controller project for CloudStack, @ddjjia can correct me if I'm wrong. Closing this PR out.