integrations/ClickUp: Add ClickUp integration script.

[PieterCK]

This script is required for the integration of ClickUp with Zulip. It is intended to be downloaded and run locally on user terminal What the script does:

• Request ClickUp's API KEY,
• Register new webhooks through their API endpoint.
• Enables the user to choose which event to be received.
• Deletes old Zulip related ClickUp webhooks when running the script multiple times.
• Appends ClickUp API KEY and team ID to the registered Zulip webhook URL to be used for callbacks.

Fixes: Issue Main ClickUp integration: PR CZO: thread

Screencast of script walkthrough: Screencast from 21-03-24 22:36:35.webm

Note:

• I ignore Ruff raising S310 because I believe it's still an open issue

[PieterCK]

@zulipbot add "buddy review"

[zulipbot]

ERROR: Label "buddy review" does not exist and was thus not added to this pull request.

[PieterCK]

@kennethnrk I think you can also take a look at this one, thank you!