Minor addition to the cvss object (#1165)

#### Related Issue: n/a

#### Description of changes:
1. Adding `vendor_name` to the `cvss` object to help represent the
source/vendor that provided the cvss scores.
2. Snippet from a sample source event from Amazon Inspector

```
"cvss": [
      {
        "baseScore": 10,
        "scoringVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
        "version": "3.1",
        "source": "UBUNTU_CVE"
      },
      {
        "baseScore": 10,
        "scoringVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H",
        "version": "3.1",
        "source": "NVD"
      }
    ],

```

---------

Signed-off-by: Rajas Panat <rajaspa@amazon.com>

CHANGELOG.md

@@ -47,6 +47,7 @@ Thankyou! -->
 * #### Objects
     1. Added `phone_number` to `user` and `ldap_person` objects. #1155
     2. Added `has_mfa` to `user` object. #1155
+    3. Added `vendor_name` to `cvss` object. #1165
 
 ### Misc
 1. Added `user.uid` as an Observable type - `type_id: 31`. #1155

objects/cvss.json

@@ -26,6 +26,10 @@
     "vector_string": {
       "requirement": "optional"
     },
+    "vendor_name":{
+      "description": "The vendor that provided the CVSS score. For example: <code>NVD, REDHAT</code> etc.",
+      "requirement": "recommended"
+    },
     "version": {
       "description": "The CVSS version. For example: <code>3.1</code>.",
       "requirement": "required"