fix: WorkloadSpread feature judgment

[ls-2018]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 48.55%. Comparing base (1f00e6b) to head (d832ed6).
Report is 21 commits behind head on master.

Files	Patch %	Lines
...validating/workloadspread_create_update_handler.go	0.00%	2 Missing ⚠️
...roller/workloadspread/workloadspread_controller.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1566      +/-   ##
==========================================
+ Coverage   47.97%   48.55%   +0.57%     
==========================================
  Files         162      163       +1     
  Lines       23491    18900    -4591     
==========================================
- Hits        11270     9177    -2093     
+ Misses      11005     8504    -2501     
- Partials     1216     1219       +3     

Flag	Coverage Δ
unittests	48.55% <0.00%> (+0.57%)	⬆️

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.

[zmberg]

@ls-2018 Creating workloadSpread fails when featureGate is false, refer code: https://github.com/openkruise/kruise/blob/master/pkg/webhook/workloadspread/validating/workloadspread_create_update_handler.go#L46

[ls-2018]

plz ignore the file directory

[zmberg]

@ls-2018 It shouldn't be allowed to be created, and when it is created it just gives an error telling him that he should open the featrueGate to do so.

[zmberg]

/lgtm

[zmberg]

/approve

[kruise-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: zmberg

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:

• OWNERS [zmberg]

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