feat: Dockerize sendgrid/rest

[graystevens]

Fixes

Resolves #45

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• Roughly followed the steps outlined in Take a rest in this docker container #45. Didn't see a clear need to update USAGE.md, so if I am wildly off track with what I have produced here, let me know 😄
• Example usage in the updated README.md.
• Included an example script within the docker folder, so that the README.md is easy to follow.

If you have questions, please send an email to Sendgrid, or file a Github Issue in this repository.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Hello @graystevens,

Thanks again for the PR!

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Team SendGrid DX