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

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[codecov]

Codecov Report

Attention: Patch coverage is 91.53439% with 16 lines in your changes missing coverage. Please review.

Project coverage is 80.13%. Comparing base (0bac4d3) to head (fc66423).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/querynodev2/delegator/delegator_data.go	83.78%	10 Missing and 2 partials ⚠️
internal/querycoordv2/dist/dist_handler.go	55.55%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #39552       +/-   ##
===========================================
+ Coverage   69.39%   80.13%   +10.74%     
===========================================
  Files         302     1476     +1174     
  Lines       27070   204352   +177282     
===========================================
+ Hits        18785   163756   +144971     
- Misses       8285    34753    +26468     
- Partials        0     5843     +5843     

Components	Coverage Δ
Client	79.44% <ø> (∅)
Core	69.39% <ø> (+<0.01%)	⬆️
Go	81.86% <87.63%> (∅)

Files with missing lines	Coverage Δ
internal/querycoordv2/checkers/index_checker.go	81.30% <ø> (ø)
internal/querycoordv2/checkers/leader_checker.go	96.83% <100.00%> (ø)
internal/querycoordv2/checkers/segment_checker.go	92.11% <100.00%> (ø)
internal/querycoordv2/meta/target_manager.go	84.37% <100.00%> (ø)
internal/querycoordv2/observers/target_observer.go	86.15% <100.00%> (ø)
internal/querycoordv2/utils/util.go	87.50% <100.00%> (ø)
internal/querynodev2/delegator/delegator.go	86.33% <100.00%> (ø)
...uerynodev2/delegator/deletebuffer/delete_buffer.go	99.20% <100.00%> (ø)
...odev2/delegator/deletebuffer/list_delete_buffer.go	100.00% <100.00%> (ø)
internal/querynodev2/delegator/delta_forward.go	68.94% <100.00%> (ø)
... and 5 more

... and 1149 files with indirect coverage changes

[weiliu1031]

rerun ut

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[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: weiliu1031
To complete the pull request process, please assign jiaoew1991 after the PR has been reviewed.
You can assign the PR to them by writing /assign @jiaoew1991 in a comment when ready.

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Needs approval from an approver in each of these files:

• internal/querycoordv2/checkers/OWNERS
• internal/querycoordv2/dist/OWNERS
• internal/querycoordv2/meta/OWNERS
• internal/querycoordv2/observers/OWNERS
• internal/querycoordv2/task/OWNERS
• internal/querycoordv2/utils/OWNERS
• internal/querynodev2/OWNERS
• pkg/proto/OWNERS
• tests/integration/OWNERS

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