fix: verify through the cache first, then delete

[tao12345666333]

Signed-off-by: Jintao Zhang zhangjintao9020@gmail.com

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What this PR does / why we need it:

For resources that will be referenced such as Upstream or PluginConfig,
when deleting, we need to check whether it is being referenced through
the cache first.
The delete operation will only be performed if the cache confirms that
it is not referenced.

fixes: #1122

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #1135 (037a08e) into master (e25abdb) will not change coverage.
The diff coverage is 50.00%.

❗ Current head 037a08e differs from pull request most recent head f3a0bb1. Consider uploading reports for the commit f3a0bb1 to get more accurate results

@@           Coverage Diff           @@
##           master    #1135   +/-   ##
=======================================
  Coverage   30.38%   30.38%           
=======================================
  Files          81       81           
  Lines        9409     9409           
=======================================
  Hits         2859     2859           
  Misses       6235     6235           
  Partials      315      315           

Impacted Files	Coverage Δ
pkg/apisix/pluginconfig.go	37.33% <40.00%> (ø)
pkg/apisix/upstream.go	39.73% <57.14%> (ø)

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