repository: optimize error handing if root.json fails to load

[AstroProfundis]

What problem does this PR solve?

This implements the code part of #1300, document updates may still be needed.

What is changed and how it works?

Keep the original error from std libraries, and display an extra warning message if the error is failed loading root.json manifest, and provide an instruction for workaround (tiup mirror set).

Check List

Tests

• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

optimize error messages when `root.json` manifest file fails to load.

[codecov-io]

Codecov Report

Merging #1303 (63d1ee6) into master (3a1296b) will increase coverage by 25.06%.
The diff coverage is 40.00%.

❗ Current head 63d1ee6 differs from pull request most recent head d899163. Consider uploading reports for the commit d899163 to get more accurate results

@@             Coverage Diff             @@
##           master    #1303       +/-   ##
===========================================
+ Coverage   26.25%   51.32%   +25.06%     
===========================================
  Files         263      289       +26     
  Lines       18947    20828     +1881     
===========================================
+ Hits         4975    10690     +5715     
+ Misses      13201     8426     -4775     
- Partials      771     1712      +941     

Flag	Coverage Δ
cluster	34.83% <0.00%> (?)
dm	26.58% <0.00%> (?)
integrate	45.51% <0.00%> (+29.01%)	⬆️
playground	24.13% <0.00%> (?)
tiup	16.50% <0.00%> (+<0.01%)	⬆️
unittest	22.77% <40.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/root.go	75.75% <0.00%> (-1.57%)	⬇️
pkg/repository/v1manifest/local_manifests.go	38.09% <0.00%> (-0.46%)	⬇️
pkg/repository/v1manifest/types.go	77.55% <60.00%> (-4.51%)	⬇️
components/playground/instance/instance.go	45.45% <0.00%> (ø)
pkg/cluster/operation/scale_in.go	50.99% <0.00%> (ø)
components/playground/instance/tidb.go	81.25% <0.00%> (ø)
pkg/cluster/operation/action.go	62.02% <0.00%> (ø)
components/playground/instance/ticdc.go	0.00% <0.00%> (ø)
pkg/cluster/operation/operation.go	69.56% <0.00%> (ø)
components/playground/instance/tiflash.go	59.09% <0.00%> (ø)
... and 189 more

---

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[lucklove]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lucklove

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[lucklove]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d899163

[codecov-commenter]

Codecov Report

Merging #1303 (bff1887) into master (150c90b) will increase coverage by 27.40%.
The diff coverage is 40.00%.

@@             Coverage Diff             @@
##           master    #1303       +/-   ##
===========================================
+ Coverage   26.26%   53.66%   +27.40%     
===========================================
  Files         263      289       +26     
  Lines       18960    20841     +1881     
===========================================
+ Hits         4980    11185     +6205     
+ Misses      13207     7854     -5353     
- Partials      773     1802     +1029     

Flag	Coverage Δ
cluster	38.34% <0.00%> (?)
dm	26.58% <0.00%> (?)
integrate	47.55% <0.00%> (+31.03%)	⬆️
playground	24.12% <0.00%> (?)
tiup	16.50% <0.00%> (-0.03%)	⬇️
unittest	22.78% <40.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/root.go	75.75% <0.00%> (-1.57%)	⬇️
pkg/repository/v1manifest/local_manifests.go	38.09% <0.00%> (-0.46%)	⬇️
pkg/repository/v1manifest/types.go	77.55% <60.00%> (-4.51%)	⬇️
pkg/cluster/operation/download.go	36.84% <0.00%> (ø)
...onents/playground/instance/tiflash_proxy_config.go	81.81% <0.00%> (ø)
components/playground/instance/tiflash.go	59.09% <0.00%> (ø)
pkg/logger/debug.go	16.66% <0.00%> (ø)
pkg/cluster/operation/scale_in.go	0.00% <0.00%> (ø)
pkg/logger/logger.go	100.00% <0.00%> (ø)
pkg/cluster/flags/debug.go	100.00% <0.00%> (ø)
... and 203 more

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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