Add use case for generation of Plain Text Content from HTML

[cmccandless]

Fixes #354

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 v4 branch.
• 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:

• Resolves Auto Generate Plain Text Content from HTML #354 by adding a use case for generating plain text when only HTML content is available.

[codecov]

Codecov Report

Merging #665 into v4 will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##               v4     #665   +/-   ##
=======================================
  Coverage   84.35%   84.35%           
=======================================
  Files          36       36           
  Lines         965      965           
  Branches      107      107           
=======================================
  Hits          814      814           
  Misses         93       93           
  Partials       58       58

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[thinkingserious]

Hello @cmccandless,

Thanks again for the PR!

It's HACKTOBERFEST! We want to show our appreciation by sending you some special Hacktoberfest swag. If you have not already, could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX

[thinkingserious]

Hello @cmccandless,

Could you please merge this against our v4 branch? Thank you!

With Best Regards,

Elmer

[cmccandless]

@thinkingserious

Could you please merge this against our v4 branch? Thank you!

Done. This PR was already merging against that branch, but I did rebase against the latest commits in v4.

[thinkingserious]

Hello @cmccandless,

Thanks again for the PR!

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[cmccandless]

Labels indicate that something further is expected of me, but I have already rebased against v4, and there are no requested changes. Is there anything else needed from me?

[thinkingserious]

Thanks for the heads up @cmccandless, this PR has been updated accordingly.

[thinkingserious]

Hello @cmccandless,

Thanks again for the PR!

We appreciate your contribution and look forward to continued collaboration. Thanks!

Team SendGrid DX