feat(55293): Add acct mapping handling gcp agentless

[wl-smith]

Issue: https://lacework.atlassian.net/browse/RAIN-55293

Description:
This is to drive feature parity with AWS for agentless workload scanning. Currently AWS Organization integrations allow for a customer to provide an account mapping file that maps to lacework sub-accounts. This is Part #2 in enabling that for GCP Agentless via terraform. Part #1 was to add the Account Mapping field to the go-sdk for Gcp Agentless.

Changes:

• Add account mapping field to gcp scanning resource
• Add functionality to update the account mapping accordingly
• Add functionality to the account_mapping_helper to look for either "gcp_projects" for the list of gcp projects or "aws_accounts" for the list of aws_accounts according to the type of integration.
• Add new integration test for GCP Org and updated example for GCP Org