Refactor config.Config to prepare for multinode

[sharifelgamal]

This PR allows a profile to have multiple MachineConfigs, to account for multiple nodes in a cluster. It also inlines KubernetesConfig under MachineConfig, so that each node in a multinode cluster can have its own k8s config.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sharifelgamal

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[codecov-io]

Codecov Report

Merging #5889 into master will decrease coverage by 0.03%.
The diff coverage is 50.61%.

@@            Coverage Diff             @@
##           master    #5889      +/-   ##
==========================================
- Coverage   36.47%   36.44%   -0.04%     
==========================================
  Files         110      110              
  Lines        8159     8161       +2     
==========================================
- Hits         2976     2974       -2     
- Misses       4794     4796       +2     
- Partials      389      391       +2

Impacted Files	Coverage Δ
cmd/minikube/cmd/config/profile_list.go	5.26% <0%> (ø)	⬆️
cmd/minikube/cmd/mount.go	8.33% <0%> (ø)	⬆️
pkg/minikube/machine/cache_images.go	5.12% <0%> (ø)	⬆️
cmd/minikube/cmd/delete.go	28.42% <0%> (ø)	⬆️
cmd/minikube/cmd/config/profile.go	0% <0%> (ø)	⬆️
cmd/minikube/cmd/logs.go	11.11% <0%> (ø)	⬆️
cmd/minikube/cmd/config/util.go	34.3% <0%> (ø)	⬆️
cmd/minikube/cmd/dashboard.go	1.76% <0%> (ø)	⬆️
cmd/minikube/cmd/ssh.go	8.69% <0%> (ø)	⬆️
cmd/minikube/cmd/tunnel.go	5.88% <0%> (ø)	⬆️
... and 8 more

[sharifelgamal]

/ok-to-test

[minikube-bot]

Error: building minikube at head: updating minikube master branch: running [git pull origin master] in /home/performance-monitor/minikube:
From https://github.com/kubernetes/minikube

• branch master -> FETCH_HEAD
  error: Your local changes to the following files would be overwritten by merge:
  go.mod
  Please commit your changes or stash them before you merge.
  Aborting
  Updating 1d0ca6c..fb5430f
  : exit status 1

[tstromberg]

It might not be perfect, but it's a start!

[sharifelgamal]

Note: we'll eventually have to deal with supporting configs in the old style, but for now this will do.