feat: Build URL with multiple instances of the same param

[agh1]

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:

A number of APIs accept what is documented as "array of string". In practice, it's a number of instances of identical URL arguments with different values.

For example from retrieving subuser reputations:

https://api.sendgrid.com/v3/subusers/reputations?usernames=myfirstsubuser&usernames=mysecondsubuser&usernames=mythirdsubuser

I updated the buildUrl() function to accept nested arrays so that you could form the above URL with the query:

$queryParams = [
  'usernames' => [
    'myfirstsubuser',
    'mysecondsubuser',
    'mythirdsubuser',
  ],
];

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

[SendGridDX]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[agh1]

Regex credit to https://stackoverflow.com/a/8171667

[agh1]

@thinkingserious per sendgrid/sendgrid-php#828 is the CLA still a thing?

[thinkingserious]

Since there has been no activity on this issue since March 1, 2020, we are closing this issue. If you are still interested in moving this PR forward, please feel free to reopen. Thank you!

[agh1]

@thinkingserious I was waiting on a response to this pull request, and I'm happy to do what's needed to move it forward if you have any feedback.

I would like to reopen it, but I don't appear to have the permission to do so.

[shwetha-manvinkurke]

LGTM! Just gotta merge changes with main

[agh1]

@shwetha-manvinkurke thanks for the review! I fixed the leading space in the doc block and rebased against main.

[thinkingserious]

Thank you!