fix: output serverless error in some environment

[czy88840616]

开放特定的环境变量下的堆栈输出，方便开发和排错。同时，增加一个特定的环境变量，用于明确需要显示错误堆栈的场景。

process.env.SERVERLESS_OUTPUT_ERROR_STACK = 'true'

[gitpod-io]

[codecov-commenter]

Codecov Report

Merging #1030 (6b623ed) into 2.x (5735ccc) will increase coverage by 0.00%.
The diff coverage is 90.90%.

@@           Coverage Diff           @@
##              2.x    #1030   +/-   ##
=======================================
  Coverage   85.97%   85.98%           
=======================================
  Files         213      213           
  Lines        8245     8247    +2     
  Branches     1613     1553   -60     
=======================================
+ Hits         7089     7091    +2     
  Misses       1107     1107           
  Partials       49       49           

Impacted Files	Coverage Δ
...es-serverless/serverless-fc-starter/src/runtime.ts	86.04% <83.33%> (+0.10%)	⬆️
...s-serverless/serverless-scf-starter/src/runtime.ts	93.15% <100.00%> (+0.09%)	⬆️

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