feat: Add an option to override SendGrid Client path version

[edwardrbaker]

Fixes

Checklist

• I acknowledge that all my contributions will be made under the project's license
• 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 development 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:

• At my job, we have a facade API that sits in between consumers and SendGrid; it does some various things that are important to our business. We overrode the host which worked fine, but it also added /v3 to the end, so that our URLs ended up being http://company-email-api.domain.com/api/v1/email/v3.
• I thought this was a simple update to give users more flexibility and should be fully backwards compatible.
• I also updated a couple pieces of the Dockerfile; The URL for prism bash script was a 404, so I updated to the current existing install script. I also added support for dos2unix, which coverts line endings. My host machine is windows, and I had lots of issues getting the docker container to run for tests because of line endings.
• I didn't apt-get remove dos2linux because I still needed to use it for the unit tests, manually.
• I am new to PHP, Docker, PHPUnit, so if I've done something wrong, please let me know

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

[thinkingserious]

Thank you @erbaker!

I've added this to our backlog for a code review.

[childish-sambino]

I'm renaming the option to be version as that's what it's called in the underlying client. Essentially, the part between the host name the start of the request path.