[Abnormal Security]: Add support for vendor-cases from API

[NateUT99]

The initial release of the Abnormal Security integration does not currently support vendor cases (/vendor-cases). These are cases that Abnormal generates when it detects an attempt to impersonation a vendor that your organization has communicated with in the past, or if the value exceeds a certain amount. The workflow seems very similar to the Account Takeover "cases" tha are already supported -- you first query to receive a list of vendor case IDs, and then you iterate through the list to collect each cases details.

The full API specification for vendor cases (/vendor-cases) is available on the Abnormal swaggerhub link below. I am also able to provide sample data if given a secure upload link.

https://app.swaggerhub.com/apis/abnormal-security/abx/1.4.3#/Vendors/get_vendor_cases