zulip-integrations: Update google oauth for google calendar integration.

[theofficialvedantjoshi]

The oauth2client library used in the google-calendar integration scripts has become deprecated. This PR updates the script to replace oauth2client with other libraries that Google is now using, specifically google-auth-httplib2 and google-auth-oauthlib.

Fixes: #847

How did you test this PR?

• Generated a client_secret.json file from a test Google Cloud application that uses the calendar API.
• Verified the authentication process and the creation of google-credentials.json in the home directory.
• Tested each flag in the argument parser by specifying the hostname and port.
• Tested the no-local-sever-auth flow in the console after obtaining an authentication code from my application's redirect URL.

Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.

[theofficialvedantjoshi]

@timabbott could you please review this PR?

[alya]

@Niloth-p It would be great to get your review on this one.