Lambda extension example script instructions

[ecraw-amzn]

Issue #, if available:

Description of changes:
Instructions for using the example script secrets-manager-agent-extension.sh to install the agent as a Lambda extension.

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.03%. Comparing base (994fe63) to head (5725924).

Additional details and impacted files

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##             main      #21   +/-   ##
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  Coverage   69.03%   69.03%           
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  Files          13       13           
  Lines        2842     2842           
  Branches       10       10           
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  Hits         1962     1962           
  Misses        880      880           

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[joebaro]

The EKS/ECS and Docker section titles are also incorrect. The EKS/ECS section should actually be called "[ Amazon EC2 ]" and the Docker section should be "[ Amazon EKS, Amazon ECS, and Docker ]" or "[ Running as a Container Side Car ]".