feat:add GetContextId func for HttpContext

[hzhswyz]

Ⅰ. Describe what this PR did

Expose the contextId property of CommonHttpCtx so that the proxywasm.SetEffectivenessContext function can be called in tickFunc

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 43.76%. Comparing base (ef31e09) to head (8f001f3).
Report is 429 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2043      +/-   ##
==========================================
+ Coverage   35.91%   43.76%   +7.85%     
==========================================
  Files          69       79      +10     
  Lines       11576    12728    +1152     
==========================================
+ Hits         4157     5570    +1413     
+ Misses       7104     6813     -291     
- Partials      315      345      +30     

see 75 files with indirect coverage changes

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[johnlanni]

LGTM