Make securityPolicy optional to allow for clean BYOC install
What does this MR do and why?
Copied from https://gitlab.com/gitlab-org/analytics-section/product-analytics/analytics-stack/-/merge_requests/206+.
The MR enables the configuration of a security policy for the Snowplow collector backend, disabled by default.
Otherwise, clean BYOC installations aren't able to function due to the collector ingress trying to assign a security policy that doesn't exist.
Documentation will likely need to be improved here to make cluster administrators more aware of this option.