feat: Support conditional LLM model mapping

[CH3CHO]

Ⅰ. Describe what this PR did

Support conditional LLM model mapping, so user can configure difference mapping rules for different consumers, a.k.a. consumer-level model aliases.

Config sample:

{
 "conditionalModelMappings": [
  {
   "consumers": [
    "test-1"
   ],
   "modelMapping": {
    "*": "my-model-1",
    "deepseek-*": "my-deepseek-1",
    "test": "my-test-1"
   }
  },
  {
   "consumers": [
    "test-3"
   ],
   "modelMapping": {
    "*": "my-model-2",
    "deepseek-*": "my-deepseek-2",
    "test": "my-test-2"
   }
  }
 ],
 "modelMapping": {
  "*": "my-model",
  "deepseek-*": "my-deepseek",
  "test": "my-test"
 }
}

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 45.81%. Comparing base (ef31e09) to head (5196ceb).
Report is 516 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1952      +/-   ##
==========================================
+ Coverage   35.91%   45.81%   +9.89%     
==========================================
  Files          69       79      +10     
  Lines       11576    12912    +1336     
==========================================
+ Hits         4157     5915    +1758     
+ Misses       7104     6650     -454     
- Partials      315      347      +32     

see 77 files with indirect coverage changes

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[johnlanni]

Need to add unit tests, and also need to provide documentation

[CH3CHO]

Done