Change shrinkIndexFlyout to page

[gaobinlong]

Description

The main changes of this PR are:

1. Change shrinkIndexFlyout to page.
2. Add unit tests for the shrink index page.
3. Modify some error message or warning message.

Issues Resolved

#468

Check List

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[codecov-commenter]

Codecov Report

Merging #476 (9729a2f) into index-operation (9e9f03c) will increase coverage by 0.03%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           index-operation     #476      +/-   ##
===================================================
+ Coverage            60.65%   60.69%   +0.03%     
===================================================
  Files                  250      250              
  Lines                 8301     8360      +59     
  Branches              1465     1477      +12     
===================================================
+ Hits                  5035     5074      +39     
- Misses                2914     2929      +15     
- Partials               352      357       +5     

Impacted Files	Coverage Δ
.../pages/Indices/containers/IndicesActions/index.tsx	72.89% <0.00%> (-3.58%)	⬇️
...ement-dashboards-plugin/public/pages/Main/Main.tsx	6.32% <0.00%> (-0.17%)	⬇️
...gement-dashboards-plugin/public/utils/constants.ts	100.00% <0.00%> (ø)
...components/ShrinkIndexFlyout/ShrinkIndexFlyout.tsx
.../Indices/components/ShrinkIndexFlyout/constants.ts
...plugin/public/pages/ShrinkIndex/utils/constants.ts	100.00% <0.00%> (ø)
.../ShrinkIndex/container/ShrinkIndex/ShrinkIndex.tsx	88.12% <0.00%> (ø)

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[Hailong-am]

how about this message The index is currently in the Red health state and may be running operations in the background. Wait until the index becomes Green to continue shrinking.

[gaobinlong]

But there are many reasons why the index is Red, like a node was left from the cluster and has not been back, or one primary shard's segment files are corrupted, so running operations maybe not a common reason, I think. Thanks for your advice, I'will think over the wording.