fix(checks): added validation for non-existing VPC endpoint policy

PR is here

Shipped in Prowler version 3.2.0.

It turned out that VPC endpoint reosource of GatewayLoadBalancer does not have policy_document attached to it thus this field value is set to None.

vpc_endpoint_connections_trust_boundaries check was not able to parse field of None that’s why it just failed with the error:

2023-02-07 18:36:25,881 [File: check.py:307] 	[Module: check]	 ERROR: vpc_endpoint_connections_trust_boundaries -- TypeError[13]: 'NoneType' object is not subscriptable

AWS CLI and userguide docs refs:

• create-vpc-endpoint

Lessons learned

Not too many, just another simple Python code fix.