refactor(cea): move cea enabled feature flag to vscode settings

[frankqianms]

workitem: https://msazure.visualstudio.com/Microsoft%20Teams%20Extensibility/_workitems/edit/31519584

[frankqianms]

@MuyangAmigo Please help review the markdownDescription content of the feature flag

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.31%. Comparing base (36d8086) to head (69344bf).
Report is 11 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #13277      +/-   ##
==========================================
+ Coverage   90.28%   90.31%   +0.03%     
==========================================
  Files         603      604       +1     
  Lines       35888    36042     +154     
  Branches     7118     7097      -21     
==========================================
+ Hits        32401    32551     +150     
  Misses       1514     1514              
- Partials     1973     1977       +4     

Files with missing lines	Coverage Δ
packages/vscode-extension/src/config.ts	94.44% <100.00%> (+0.15%)	⬆️
packages/vscode-extension/src/constants.ts	100.00% <100.00%> (ø)

... and 15 files with indirect coverage changes