scheduler: remove the restriction that reservation cannot be preempted

[eahydra]

Ⅰ. Describe what this PR does

Remove the restriction that reservation cannot be preempted. If users create reservation with priority, and mark the reservation is preemptible, the reservation can be preempted, otherwise, the reservation cannot be preempt since the priority is the highest by default.

Ⅱ. Does this pull request fix one issue?

fix #1856 implement #1887

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 67.50%. Comparing base (c0374ef) to head (ad7f84d).
Report is 1 commits behind head on main.

Files	Patch %	Lines
pkg/scheduler/plugins/reservation/plugin.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1859      +/-   ##
==========================================
- Coverage   67.51%   67.50%   -0.02%     
==========================================
  Files         416      416              
  Lines       46354    46333      -21     
==========================================
- Hits        31297    31276      -21     
- Misses      12778    12781       +3     
+ Partials     2279     2276       -3     

Flag	Coverage Δ
unittests	67.50% <88.88%> (-0.02%)	⬇️

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[eahydra]

@buptcozy @xulinfei1996 Do you have any comments?

[xulinfei1996]

/lgtm

[buptcozy]

/lgtm

[buptcozy]

/approve

[FillZpp]

/lgtm

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: buptcozy, FillZpp

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• pkg/scheduler/OWNERS [buptcozy]
• pkg/util/OWNERS [FillZpp]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment