feat: support variable in ApisixRoute exprs scope

[AlinsRan]

Type of change:

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

What this PR does / why we need it:

• feature request: ApisixRoute resources use vars in Route #1376

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 #1466 (4782a05) into master (5570d28) will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1466      +/-   ##
==========================================
- Coverage   41.35%   41.23%   -0.13%     
==========================================
  Files          82       82              
  Lines        7261     7283      +22     
==========================================
  Hits         3003     3003              
- Misses       3911     3933      +22     
  Partials      347      347              

Impacted Files	Coverage Δ
pkg/providers/apisix/translation/apisix_route.go	31.51% <0.00%> (-0.27%)	⬇️
...providers/gateway/translation/gateway_httproute.go	48.61% <0.00%> (-3.89%)	⬇️

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