Add stage_index field at BuildQuickSyncStagesRequest

[Warashi]

What this PR does / why we need it:

We need stage_index when multiple plugins can return QUICK_SYNC Stages.

Which issue(s) this PR fixes:

Part of #4980

Does this PR introduce a user-facing change?:

• How are users affected by this change:
• Is this breaking change:
• How to migrate (if breaking change):

[khanhtc1202]

🆗

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.91%. Comparing base (c3386cf) to head (f39e69a).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5229   +/-   ##
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  Coverage   22.91%   22.91%           
=======================================
  Files         419      419           
  Lines       45321    45321           
=======================================
  Hits        10385    10385           
  Misses      34139    34139           
  Partials      797      797           

Flag	Coverage Δ
	22.91% <ø> (ø)

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