[client] Support of KEV field for vulnerability entity (#7390)

[ValentinBouzinFiligran]

Proposed changes

• cisa kev key added on creation mutation and vulnerability query

Related issues

• Support of "KEV" field for vulnerability entity opencti#7390

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

• opencti: [frontend/backend] Support of "KEV" field for vulnerability entity (#7390) opencti#7646

[SouadHadjiat]

I think we also need to support this field in in import_from_stix2

[helene-nguyen]

All good to me, tested locally following these steps:

• Added it in custom properties when creating the stix object for a Vulnerability

• Check the stix object

• Run the connector, no error and field properly set