re-introduce and fix declcfg.Meta unmarshal error

[joelanford]

Description of the change:
Re-introduce pretty-printing of json.Unmarshal errors encountered with unmarshaling declcfg.Meta objects.

Motivation for the change:
Prior to #1094, we had some nice pretty printing of JSON unmarshaling errors. That pretty printing also had a bug that caused an index out-of-bounds panic.

In #1094, we inadvertently stopped using the pretty-printing. This technically solved the panic bug, but we lost the pretty-printing as well.

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[codecov]

Codecov Report

Merging #1109 (dfc71ec) into master (b51aaf0) will increase coverage by 0.27%.
The diff coverage is 85.71%.

❗ Current head dfc71ec differs from pull request most recent head b991fa8. Consider uploading reports for the commit b991fa8 to get more accurate results

@@            Coverage Diff             @@
##           master    #1109      +/-   ##
==========================================
+ Coverage   52.35%   52.63%   +0.27%     
==========================================
  Files         107      108       +1     
  Lines        9688     9703      +15     
==========================================
+ Hits         5072     5107      +35     
+ Misses       3674     3654      -20     
  Partials      942      942              

Impacted Files	Coverage Δ
pkg/cache/cache.go	32.35% <0.00%> (ø)
alpha/declcfg/load.go	74.05% <62.50%> (-1.28%)	⬇️
alpha/template/composite/builder.go	83.44% <80.00%> (ø)
alpha/declcfg/errors.go	91.89% <91.89%> (ø)
alpha/action/render.go	65.02% <100.00%> (ø)
alpha/declcfg/declcfg.go	78.94% <100.00%> (+32.07%)	⬆️
alpha/template/composite/composite.go	78.70% <100.00%> (ø)
pkg/cache/json.go	53.15% <100.00%> (ø)

... and 2 files with indirect coverage changes

[joelanford]

/hold
i think there's still a bug here with the marker placement.

[joelanford]

/hold cancel

Beefed up the logic, added unit tests to prove things work and to prevent regressions.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: grokspawn, joelanford

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• OWNERS [grokspawn,joelanford]

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[grokspawn]

/lgtm