Automatically fix old configs by default

[nkubala]

This adds a hook in the runner to automatically try and upgrade older configs to the latest version before running skaffold. This means users with older configs will no longer be required to run skaffold fix to run skaffold as we upgrade the config.

I'll leave skaffold fix in, in case anybody wants to use it to upgrade their config and overwrite it in their repo.

Fixes #1257

[balopat]

With this change I would like to cover all the upgrades with unit tests and hunt down if there are any issues.

[codecov-io]

Codecov Report

Merging #1259 into master will increase coverage by 1.76%.
The diff coverage is 5.26%.

@@            Coverage Diff             @@
##           master    #1259      +/-   ##
==========================================
+ Coverage   42.42%   44.19%   +1.76%     
==========================================
  Files          96      104       +8     
  Lines        4247     4614     +367     
==========================================
+ Hits         1802     2039     +237     
- Misses       2269     2366      +97     
- Partials      176      209      +33

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/deploy.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/run.go	0% <0%> (ø)	⬆️
pkg/skaffold/schema/versions.go	47.22% <0%> (-17.65%)	⬇️
cmd/skaffold/app/cmd/dev.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/diagnose.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/runner.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/delete.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/build.go	0% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/fix.go	19.35% <100%> (ø)	⬆️
pkg/skaffold/schema/v1alpha2/upgrade.go	68.88% <0%> (ø)
... and 8 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3465168...558ac9f. Read the comment docs.

Added unit tests for all config upgrades

[balopat]

LGTM, thank you!