chore: rev default etcd version to 3.4.13

[jackfrancis]

Reason for Change:

This PR updates the default etcd version to v3.4.25 or control plane nodes.

Ref:

https://github.com/etcd-io/etcd/releases/tag/v3.4.13

Issue Fixed:

Fixes #3663

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3748 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3748   +/-   ##
=======================================
  Coverage   73.19%   73.19%           
=======================================
  Files         148      148           
  Lines       25394    25394           
=======================================
  Hits        18587    18587           
  Misses       5671     5671           
  Partials     1136     1136           

Impacted Files	Coverage Δ
pkg/api/vlabs/validate.go	80.15% <ø> (ø)
pkg/engine/templates_generated.go	53.42% <ø> (ø)

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[jackfrancis]

So, after going through this prototype exercise to make etcd 3.4 work, I strongly suspect that maintaining a common configuration surface area that will work across all the currently supported etcd versions is not tenable. We should strongly consider introducing 3.4 as a "you can't go back to 3.3 or prior" change.

cc @Michael-Sinz @devigned

[Michael-Sinz]

Interesting - we should look at a what this buys us. We have a lot of miles on 3.3.x but we know that there are demons in there.

We should ask the aks team what they saw with 3.4 vs 3.3 in their setup. However, there have been critical fixes that went into 3.4 first and then backported to 3.3. For example, you really don't want to be at or before 3.3.13 due to at least one critical issue that was first fixed in 3.4 and then finally backported to 3.3.14

[mboersma]

Just fyi, as of Kubernetes 1.19.1, etcd server 3.4.13 is the default.

[mboersma]

/lgtm

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[jackfrancis]

This PR is not compatible w/ etcd 3.3 and below

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[bridgetkromhout]

Closing per @jackfrancis, given AKS Engine deprecation.