chore: deprecate rescheduler addon

[jackfrancis]

Reason for Change:

This PR deprecates and removes the long-obsolete rescheduler addon. The justification for removing it entirely is that it is ~3 years out of date, and deprecated upstream as of Kubernetes v1.10.0. We want to prevent folks from installing it on new clusters as the functional outcomes from running this addon on your cluster is unknown.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

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

Notes:

[codecov]

Codecov Report

Merging #4275 (8ea891e) into master (f220f16) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4275   +/-   ##
=======================================
  Coverage   72.07%   72.07%           
=======================================
  Files         141      141           
  Lines       21686    21665   -21     
=======================================
- Hits        15630    15616   -14     
+ Misses       5106     5099    -7     
  Partials      950      950           

Impacted Files	Coverage Δ
pkg/api/addons.go	98.07% <ø> (-0.03%)	⬇️
pkg/api/common/const.go	100.00% <ø> (ø)
pkg/api/k8s_versions.go	100.00% <ø> (ø)
pkg/api/types.go	92.85% <ø> (-0.02%)	⬇️
pkg/engine/artifacts.go	98.93% <ø> (-0.03%)	⬇️
pkg/engine/templates_generated.go	43.80% <ø> (+0.38%)	⬆️
pkg/api/vlabs/validate.go	81.42% <100.00%> (+0.07%)	⬆️

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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