cluster: allow continue editing when new topology has errors

[AstroProfundis]

What problem does this PR solve?

In edit-config, if the new topology fails parsing or validation, it just returns error and exists, changes are not saved and lost.

What is changed and how it works?

Prompt the user to choose to continue editing or not.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Code changes

• Has exported function/method change

[codecov-commenter]

Codecov Report

Merging #624 into master will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #624      +/-   ##
==========================================
+ Coverage   47.78%   47.90%   +0.11%     
==========================================
  Files         225      225              
  Lines       16728    16747      +19     
==========================================
+ Hits         7993     8022      +29     
+ Misses       7616     7605      -11     
- Partials     1119     1120       +1     

Flag	Coverage Δ
#coverage	47.90% <ø> (+0.11%)	⬆️

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

Impacted Files	Coverage Δ
...cap/tiup/components/cluster/command/edit_config.go	37.50% <0.00%> (-6.95%)	⬇️
go/src/github.com/pingcap/tiup/pkg/cliutil/tui.go	68.51% <0.00%> (-2.64%)	⬇️
...hub.com/pingcap/tiup/components/playground/main.go	80.83% <0.00%> (+0.59%)	⬆️
...m/pingcap/tiup/components/playground/playground.go	30.33% <0.00%> (+1.12%)	⬆️
...c/github.com/pingcap/tiup/pkg/cluster/api/pdapi.go	55.27% <0.00%> (+1.86%)	⬆️
.../pingcap/tiup/components/playground/utils/utils.go	27.65% <0.00%> (+27.65%)	⬆️

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[lucklove]

LGTM

[ti-srebot]

/run-all-tests