enhance: Remove QueryCoord's scheduling of L0 segments

[weiliu1031]

issue: #39551
This PR remove querycoord's scheduling of l0 segments:

• only load l0 segment when watch channel
• only release l0 segment when release channel or sync data distribution

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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• internal/querycoordv2/checkers/OWNERS
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• internal/querycoordv2/observers/OWNERS
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• internal/querynodev2/OWNERS
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.40%. Comparing base (f0b7446) to head (96156dc).
Report is 1 commits behind head on master.

❌ Your project check has failed because the head coverage (69.40%) is below the target coverage (77.00%). You can increase the head coverage or adjust the target coverage.

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HEAD has 1 upload less than BASE

Flag	BASE (f0b7446)	HEAD (96156dc)
	2	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #39552       +/-   ##
===========================================
- Coverage   80.10%   69.40%   -10.70%     
===========================================
  Files        1465      302     -1163     
  Lines      203148    27065   -176083     
===========================================
- Hits       162733    18785   -143948     
+ Misses      34602     8280    -26322     
+ Partials     5813        0     -5813     

Components	Coverage Δ
Client	∅ <ø> (∅)
Core	69.40% <ø> (ø)
Go	∅ <ø> (∅)

see 1163 files with indirect coverage changes

[weiliu1031]

rerun ut

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