add enableProfiling, cold-start-tracing and lambda-authorizer related env variables

[joeyzhao2018]

What does this PR do?

Version 0.5.4 was deployed to the staging bucket and tested with a hello-world example function.

The parameters successfully showed up as expected and the related features are working as expected.

Motivation

Add the missing env variables.

Testing Guidelines

Ran the serverless/tools/installation_test.sh and then create an example SAM project that uses the staged macro.

Additional Notes

Types of changes

• [ ] Bug fix
• [ ] New feature
• [ ] Breaking change
• [x] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [ ] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog

[codecov-commenter]

Codecov Report

Merging #84 (a65dce6) into master (ea21073) will increase coverage by 0.24%. The diff coverage is 100.00%.

:exclamation: Current head a65dce6 differs from pull request most recent head 1f75351. Consider uploading reports for the commit 1f75351 to get more accurate results

@@            Coverage Diff             @@
##           master      #84      +/-   ##
==========================================
+ Coverage   93.01%   93.25%   +0.24%     
==========================================
  Files           7        7              
  Lines         501      519      +18     
  Branches      117      123       +6     
==========================================
+ Hits          466      484      +18     
  Misses         26       26              
  Partials        9        9              

Impacted Files	Coverage Δ
serverless/src/env.ts	97.24% <100.00%> (+0.54%)	:arrow_up:

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