Integration of nodemailer-sendgrid-transport

[Berkmann18]

Fixes

Closes nodemailer-sendgrid-transport#67.

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 inline documentation to the code I modified

Short description of what this PR does:

• Integrates the then nodemailer-sendgrid-transport package as a sub-package among others (while having it match and follow the structure/convention used by other sub-packages).
• Help with PRs such as NST#67, NST#64 and issues such as NST#65 and NST#25.

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

Note: (as discussed in the PR mentioned above): the npm test fails due to the usage of the former sendgrid package in this codebase with some API changes and some sub-packages not available yet on NPM (causing all require('@sendgrid/xxx') to fail).

[thinkingserious]

This is awesome, thanks! I've added this to our backlog for review.

[thinkingserious]

Hello @Berkmann18,

Thanks again for the PR!

We want to show our appreciation by sending you some swag. Could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX

[Berkmann18]

@thinkingserious You're welcome.
I've had a look at it and I'm wondering what the "Attention" field is for, is that to do with what I did, or something to avoid putting/using on the t-shirt?

[gian1200]

Was this PR rolled back? Can't find a not vulnerable version of nodemailer-sendgrid-transport that works with SendGrid.