[FEATURE] Wrapper for Google Calendar API

[TheCedarPrince]

Hi GoogleCloud Maintainers,

I apologize for the random PR out of the blue but I had the impression that GoogleCloud.jl would be the ideal place to contribute new features/wrappers too for the suite of Google Cloud Platform products based on the documentation. I have been developing some "homemade" features for Google Calendar's API that utilizes HTTP payloads. I opened this PR in the hopes of building out support for this API within GoogleCloud.jl as I need it for another project. Here is how it currently can be invoked:

import Google: Calendar.Calendars

calendar_id = "primary"
key = "API KEY"
client_id = "GCP Client ID"
access_token = "ya29. ... REST OF ACCESS TOKEN"

Calendars.get(calendar_id, key, client_id, access_token)

Which would return a JSON Calendar Resource payload that could be parsed via JSON3 or otherwise:

HTTP.Messages.Response:
"""
HTTP/1.1 200 OK
Expires: Wed, 31 May 2023 20:04:14 GMT
Date: Wed, 31 May 2023 20:04:14 GMT
Content-Type: application/json; charset=UTF-8
Content-Length: 326
Cache-Control: private, max-age=0, must-revalidate, no-transform
ETag: "redacted"
Vary: Origin, X-Origin, Referer
Server: ESF
X-XSS-Protection: 0
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
Alt-Svc: h3=":443"; ma=2592000,h3-29=":443"; ma=2592000

{
 "kind": "calendar#calendar",
 "etag": "\"redacted\"",
 "id": "redacted",
 "summary": "JZ Calendar",
 "description": "My main calendar - where all the magic happens",
 "timeZone": "America/New_York",
 "conferenceProperties": {
  "allowedConferenceSolutionTypes": [
   "hangoutsMeet"
  ]
 }
}
"""

---

I paused for now in adding any additional features/functionality as I wanted to get some feedback before proceeding and also ran into some issues on integrating with the rest of GoogleCloud.jl. Here were the points I was thinking about and wanted get y'all's feedback on:

1. How can I set-up authentication using the package already? I want to use the authentication tools you have but I am unsure how to generate access tokens and integrate with the functions I have already built.
2. If you look at the functions I created, I basically created a 1-to-1 wrapper to the calendar API's corresponding function. I was rather ham-fisted with just manually mapping everything over but am not too sure if there is a more elegant way to build GET/POST requests via HTTP.jl (I was looking at the query kwarg but I am not sure if that would be too low-level).
3. I don't know how to build effective tests for this module -- would we want to set-up a dummy account for testing or how would you all do it?
4. I introduced submodules to organize things better since in this case, I found multiple dispatch (in a rare circumstance) a bit more convoluted here than having a more OOP/module based approach.

I apologize if this should not be supported within GoogleCloud.jl but I thought I'd try adding here first before making a separate package for the calendar. Otherwise, I look forward to your feedback! Thanks!