fgt_asg: storage bucket name is not globally unique

[bartekmo]

Storage bucket names must be globally unique. Two deployments in the same project need to have different prefixes thus we will not see the conflict, but deployments in different projects can use the same prefix triggering conflict on the bucket name.

Suggested solution would be to:

1. generate random suffix
2. add it to the bucket name
3. pass bucket name as variable to function
4. modify function top accept it.

[bartekmo]

NOTE: requires function change

As the cloud function uses a hard-coded bucket name based on PROJECT_PREFIX variable (main.py:219), the proposed change requires modification of the function itself.