Handle openai change of api base for just embeddings

[keeganmccallum]

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[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: keeganmccallum
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[sre-ci-robot]

Welcome @keeganmccallum! It looks like this is your first PR to zilliztech/GPTCache 🎉

[SimFG]

@keeganmccallum thank your pr, please make the dev as the target branch

[codecov]

Codecov Report

Merging #495 (071408c) into dev (a3328f2) will decrease coverage by 0.02%.
The diff coverage is 85.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #495      +/-   ##
==========================================
- Coverage   94.20%   94.18%   -0.02%     
==========================================
  Files          94       94              
  Lines        3898     3903       +5     
==========================================
+ Hits         3672     3676       +4     
- Misses        226      227       +1     

Files Changed	Coverage Δ
gptcache/embedding/openai.py	94.11% <85.71%> (-2.44%)	⬇️