[FEATURE] add environmental variables for local connection

[nghhoese]

Summary:

Right now the way to start a local session is through changes in your code, would like to set an env variable to declare a local session like DYNAMO_LOCAL or DYNAMOOSE_LOCAL_SESSION=true or false something like that.

Code sample:

Schema

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Model

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General

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Environment:

Operating System: Docker
Operating System Version: Custom Image
Node.js version (node -v): latest
NPM version: (npm -v): latest
Dynamoose version: latest

Other information (if applicable):

Other:

• [ x ] I have read through the Dynamoose documentation before posting this issue
• [x ] I have searched through the GitHub issues (including closed issues) and pull requests to ensure this feature has not already been suggested before
• [ x] I have filled out all fields above
• [ x] I am running the latest version of Dynamoose